Bonus Slots

An Introduction to the Mechanics of Bonus Slots

Slots are the most widespread type of game in both online and brick-and-mortar casinos, and given their simplicity, it is not difficult to see why. Practically anyone can play because the rules are easy to learn, and no previous experience or skill is required. Slots come in many forms, and the wide variety of themes and betting limits is sure to meet the expectations of even the most demanding slot enthusiasts.

However, one category of online slots is in especially high demand among fans of the game: the so-called bonus slots. As the name suggests, these games come with various additional features that can create more ways to win and make gameplay more engaging. We have outlined some of the most important features of online bonus slots below, but first, let us start with a few words about their interfaces, gameplay, and visual characteristics.

Best Rated Casinos for United States 

1. 
   Sign Up Bonus
   Up to $500
   400% Bonus!
   9.7
   REVIEW
   GET BONUS
2. 
   Sign Up Bonus
   Up to $3500
   350% Bonus!
   9.4
   REVIEW
   GET BONUS
3. 
   Sign Up Bonus
   Up to $3000
   300% Bonus!
   9.3
   REVIEW
   GET BONUS

Gameplay and Interface

As the name indicates, this slot variation offers bonus games and other special features as additional incentives for players. Most advanced five-reel slots available in the game collections of established online casinos fall into this category. WMS was the first slot manufacturer to introduce an additional bonus game on a separate screen with Reel ‘Em In.

This innovation can mainly be attributed to the introduction of microchip technology in video slots, which enabled developers to broaden their scope and add greater entertainment value to their games. In addition, bonus slots allow for greater player interaction because their bonus games and features typically revolve around the slot’s storyline and general theme.

Apart from the additional games and features, bonus slots are not significantly different from less advanced classic slots. Players will notice few major differences in terms of gameplay and interface. They must again adjust the coin value and multiplier, or the number of coins per line, and activate the paylines on which they wish to bet. If the paylines are fixed, players must bet on all of them.

Take a look at a bonus slot’s paytable, and you will immediately notice that some additional symbols are listed there. Some may trigger a bonus game, while others may unlock a predetermined number of free spins. Please note that bonus games typically load on a separate screen and are not part of the base game.

Screenshot of Slot Wild North Bonus Game Paytable

In bonus slots, players can usually trigger a round of free spins, but the number of extra spins varies by game. Bonus games and free spins do not require players to place additional bets. However, the payouts depend on the initial bet used to trigger the bonus feature.

Bonus slots are considered more elaborate, especially in terms of graphics and animations. The visuals can be realistic and crisp, while detailed sound effects add another dimension to the games. The storylines may also be more complex, with players sometimes required to complete various achievements.

Some bonus slot titles allow players to save their progress during a bonus round and continue where they left off the next time they load the game. In addition, some bonus slots are based on popular movies or TV series. These typically begin with a short animated introductory clip and may feature footage from the production when the player unlocks the bonus round or hits a winning combination.

Types of Bonus Games in Slots

One important thing to remember is that there is little players can do to influence when a bonus game is triggered. Bonus games are typically unlocked by landing a specific number of bonus symbols or by hitting three or more scatters on the reels. The additional games found in bonus slots can be divided into several categories, including pick-to-win games, pick-to-match games, wheel games, and free spins.

Pick-to-Win Games

This is one of the most common types of bonus games found in advanced slot variations. These games are straightforward and therefore easy to play. Pick-to-win bonus games are typically unlocked when the player lands a given number of bonus symbols during the base game.

In many cases, the bonus symbols must land on specific reels to trigger the mini-game. This is the case with Betsoft’s Dr. Jekyll & Mr. Hyde, where players must land the bonus symbols on the second, third, and fourth reels for the bonus game to start. In NetEnt’s Bloodsuckers slot, players must land three or more bonus symbols on an active payline to trigger the bonus game and then select several vampire coffins containing specific numbers of extra coins.

Once the pick-to-win game is unlocked, players usually need to click specific locations on the screen to uncover different prizes or multipliers for the amount won on the last base-game spin. At the end of the pick-to-win bonus game, players receive the winnings accumulated during the bonus round. Players often choose one or more boxes or treasure chests containing hidden cash prizes or multipliers, although the exact format varies by slot.

Pick-to-Match Games

Another popular feature found in some bonus slots is the pick-to-match game. It resembles the previously described pick-to-win variation, but there are a few differences. The bonus game is again unlocked by lining up a given number of special symbols on the reels.

However, players are given the option to pick two or more matching items or cash amounts hidden in different locations on the bonus game’s screen. If successful, they receive the corresponding payout based on the symbols they have matched.

In some instances, players can win one of several progressive jackpots when they unlock the pick-to-match bonus game. They must again uncover several matching symbols, each of which is associated with one of the progressive jackpots. This was the case with some slots from Playtech’s popular but now-defunct Marvel series.

Wheel Bonus Games

Like most bonus games, those that involve spinning a wheel are triggered without requiring any skill. After players land the bonus symbols that unlock the wheel game, they simply set the wheel in motion.

The wheel is divided into several segments, each containing a specific number of extra coins or a multiplier that can increase the player’s winnings from the last base-game spin. Occasionally, the wheel may reward players with free spins. Once the wheel comes to rest, the player collects the prize indicated by the pointer.

Free Spins Rounds

These are among the most common and basic bonus features found in video slots. Free spins are usually triggered when players land several scatter symbols across the reels. The number of spins awarded often depends on how many special symbols appear. Bonus spins are typically played at the same bet amount used before they were triggered. Some include multipliers that can increase winnings, but this varies by game.

Depending on the selected slot, players may be able to retrigger additional free spins during the bonus round. Free spins are often retriggered when the player lands the same number of bonus symbols that originally unlocked the feature. Players cannot usually retrigger spins indefinitely because most bonus slots impose a limit on the number of spins available in a single bonus round.

Community Bonuses

Game designers have attempted to make slot play more interactive and social by introducing community-style bonuses in which several players can participate simultaneously.

The first slot of this type was Bonus Road Rally, designed by A. C. Coin. It featured a racetrack with ten cars, one for each game linked to the Bonus Road Rally bank. Players advanced the cars around the racetrack by placing bets. The player whose vehicle crossed the finish line first received the largest bonus.

Some community-style slots enable multiple players to win a share of the bonus prizes. One example is Monopoly Big Event by WMS Gaming. Launched in 2005, the slot allowed players to participate in a side board game, rolling virtual dice to advance and earn credits for landing on different Monopoly properties.

WMS also introduced the Reel ‘Em In: Compete to Win slot, in which participating players competed to catch fish and collect bonus winnings. Prize values depended on the size of the fish caught. At the end of the bonus round, the player with the largest bonus win won the derby and received an additional prize.

Skill-Based Bonuses

In slots with skill-based bonuses, a specific percentage of the overall theoretical return depends on the player’s performance during the bonus game. However, the long-term odds still favor the house. One example is IGT’s Tully’s Treasure Hunt, in which players use a joystick to navigate a turtle through a sea maze and collect bonus credits.

The bonuses increase when the turtle passes through certain symbols. IGT also designed the Centipede slot, in which players again use a joystick, along with additional buttons, to shoot at a moving centipede. Players who defeat the creature progress to a second level with greater difficulty and larger bonuses.

Mystery Bonuses

Mystery bonuses can add excitement because the bonus games are triggered at random rather than by a specific combination of symbols on the reels. These mystery triggers are common in multilevel progressive jackpot games, although some slots with fixed jackpots also offer them.

The random number generator launches the mystery bonus without an advance indication that the feature is about to start. Some mystery bonuses begin at randomly selected times, while others commence after players have wagered a randomly selected number of credits. In progressive slots, the bonus game can trigger when the prize pool reaches a randomly selected amount.

Other Important Features of Bonus Slots

Most bonus games provide an extra incentive to continue playing and are designed to maintain players’ interest. However, bonus slots can include additional special features that diversify gameplay and create more ways to win. You can find more detailed information about these features below.

Wilds

Wilds are commonly incorporated into bonus slots and have become a standard feature in many such games. They are considered some of the most valuable symbols in video slots because they serve a similar purpose to wild cards in some variations of video poker. In other words, wilds can replace other symbols on the reels and help players complete more winning combinations. However, wilds generally cannot substitute for scatter or bonus symbols. Wilds may also need to land on specific reels or active paylines to contribute to a payout.

There are many subtypes of wild symbols, and their behavior varies depending on the slot. For instance, expanding wilds can cover all positions on the reel on which they land, helping to produce more winning combinations. Shifting wilds remain on the screen for subsequent spins and move to different reel positions after each round.

Walking wilds resemble shifting wilds but can move to the left, the right, or sometimes in both directions. Stacked wilds are also popular because multiple wild symbols appear on top of one another and can cover an entire section of a reel.

Sticky wilds are popular among slot enthusiasts. They function like regular wilds by replacing symbols on the reels and helping players form winning combinations. However, this wild variation remains, or “sticks,” on the reels for a predetermined number of subsequent spins. Sticky wilds are usually found during free spins or as part of another special feature.

Transferring wilds are normally available in slots featuring several sets of reels. Such games often include one large reel set and two smaller sets positioned to the side. Fire Queen by WMS is an example, featuring one larger 6×3 reel grid and two smaller 2×2 reel sets on its left side. When a wild symbol lands on the first reel set, it transfers to the corresponding position on the other reel grids, increasing the chances of forming winning combinations.

Scatters

Scatters are among the most valuable features found in bonus slots. Unlike wilds, scatters do not necessarily need to land on specific paylines to produce a payout. They also serve a different purpose. Landing several scatter symbols anywhere on the reels can unlock additional features, such as free spins or bonus games.

At times, scatters function like regular symbols and pay for winning combinations. In some games, they can also increase winnings by acting as multipliers. Some slots feature expanding scatters, which function similarly to expanding wilds but do not substitute for other symbols. They usually appear during free spins.

The software selects a symbol at random, and if it lands during the special feature, it expands to cover the entire reel. Expanding scatters can lead to larger wins, especially in five-reel games when they land on all five reels. Slots with expanding scatters include Book of Ra by Novomatic and Luxor Valley by Viaden.

Tumbling Reels

Slots that use the tumbling reels format resemble traditional machines until a winning combination appears. The software awards the corresponding payout according to the paytable. The symbols involved in the winning combination then disappear, allowing new icons to fall into their positions. The process usually continues until no new winning combination is formed. In some games, however, the reels can tumble only a preset number of times.

Many slots that use the tumbling mechanic also feature multipliers that increase with each successive win. Tumbling reels, also known as cascading reels, offer two main benefits to players. First, they provide an opportunity to register multiple consecutive wins from a single bet.

Second, the format adds excitement to each spin because there is no way to know how long a sequence of winning combinations will last. This mechanic appears in games such as Betsoft’s Birds!, NetEnt’s Gonzo’s Quest, Golden Ticket by Play’n GO, and Thunderkick’s Esqueleto Explosivo.

Split Symbols

Split symbols function as two individual icons occupying the same position on the reels. In effect, the player lands two icons simultaneously, which can result in larger wins. Regular icons, scatters, and wilds can all appear as split symbols, depending on the slot. When they appear as scatters, they can improve the chances of triggering a bonus feature.

One benefit of split symbols is that they can increase payouts when they land on two or three reels along an active payline. Filling the reel grid with these symbols can produce a substantial payout. However, wilds commonly cannot substitute for special icons, including split symbols.

Another disadvantage is that games with split icons often have medium or high volatility, which can make them unsuitable for players with limited bankrolls. This feature appears in slot releases such as Microgaming’s So Much Candy, Shadow of the Panther by High 5 Games, and Perfect Gems by Play’n GO.

Respin Feature

Some slots include a respin feature that allows players to spin a selected reel independently. The respin comes at a cost, but the exact amount depends on the selected reel and the symbols displayed on it. The applicable amounts appear below the corresponding reels. The other four reels remain locked in place during the respin.

Many slots with this feature allow players to respin the selected reel multiple times in an attempt to complete a desired combination. The feature can be useful when a player is one symbol short of forming five matching symbols. In many cases, only wins involving the respun reel are paid. Slots with this respin option include Microgaming’s Bikini Party and Reel Gems.

In some games, such as NetEnt’s popular Starburst, the respin feature comes at no extra cost. Players trigger it by landing a specific symbol combination consisting of wilds on the second, third, and fourth reels. When this happens, all five reels automatically respin, potentially resulting in additional winning combinations. Unlike the paid feature, the number of free respins is limited, in this case to three.

Multiplier Symbols

Some bonus slots include special multiplier symbols. Whenever these symbols land on an active payline, they multiply the payout for a winning combination by a predetermined amount. Sometimes, multipliers are available only to players who have wagered the maximum number of coins allowed in the game.

Multipliers are typically incorporated into free spins or bonus games and are less common in the base game. Some symbols function as both wilds and multipliers, replacing other symbols while also increasing the resulting payout.

Bonus Buy Feature

Sometimes, bonus games are difficult to trigger, or players may not want to wait for the required symbols to land. In some slot releases, the bonus buy feature allows players to trigger a bonus directly from the base game by paying a specified amount.

The exact cost varies from one slot to another. For instance, the free spins feature in Pragmatic Play’s Voodoo Magic costs 80x the current overall wager. In Quickspin’s Golden Glyph 2, players can access the free spins feature by purchasing one, two, or three wilds.

The theoretical return of the buy feature ranges from 96.30% to 96.60%, depending on how many wilds are purchased to unlock it. Although buying direct access to a bonus may seem tempting, players should use this option cautiously.

The payout from the bonus may be lower than the amount originally paid to activate the feature. This option is also available in slots such as Sticky Bandits 3 by Quickspin, Templar Tumble by Relax Gaming, and Elemento by Fantasma Games.

Top 5 Bonus Slots

Bonus slots can offer more than standard winning combinations by including features such as respins, free spins, wild multipliers, and interactive bonus rounds. Below, we review five bonus slots with distinctive themes and feature sets. Each game provides a different combination of mechanics, betting options, and bonus features for players to consider.

1. Money Train 3 Slot

Money Train 3 is a Relax Gaming slot set in a futuristic world. It builds on the previous Money Train releases with new features and a maximum win potential of 100,000x the bet. The game combines high volatility with several bonus mechanics designed around its train-themed setting.

Screenshot of Money Train 3 Slot

Money Train 3 Slot Details

Pros and Cons

Symbols and Theme

Money Train 3 moves away from the steampunk and Wild West themes of its predecessors and places the action in a futuristic train station. Available across different devices, the game includes lower-value suit symbols and higher-value character symbols. Wild and scatter symbols contribute to the game’s bonus mechanics.

Slot Features

The Wild Symbol and Respin feature work together, with respins providing another chance to form a winning combination after a non-winning spin. The Money Cart Bonus Round includes special symbols that can unlock additional reels and reset respins.

Bonus Buy

The Bonus Buy feature provides direct access to the bonus game, with options suited to different strategies and budgets. This feature has an RTP of 96.50%.

Money Train 3 combines a futuristic setting with several bonus mechanics and high win potential.

2. The Dog House Megaways Slot

The Dog House Megaways is Pragmatic Play’s Megaways adaptation of The Dog House. The game offers between 64 and 117,649 ways to win and has a maximum win potential of 12,305x the stake. Its features include multiplier wilds and two free spins options, including the Sticky Wilds Free Spins feature. The related title The Dog House Multihold was released in February 2023 and also includes sticky wilds.

Screenshot of The Dog House Megaways Slot

The Dog House Megaways Slot Details

Pros and Cons

Symbols and Theme

The Dog House Megaways uses a cartoon-style suburban setting, with the reels placed inside a doghouse. The symbols range from lower-value card ranks to four higher-value dog characters, including a dachshund and a Rottweiler. The Dog House symbol acts as the wild and can substitute for other symbols to help complete winning combinations.

Slot Features

Wild Multipliers Feature – Wilds can appear on reels 2 through 5, with each wild potentially carrying a 2x or 3x multiplier. When multiple wilds contribute to the same combination, the combined multiplier can reach 126x.

Free Spins Features – Landing three or more paw-print scatters allows players to choose between the Raining Wilds and Sticky Wilds Free Spins features. Each option provides a different free spins format. Outside the UK, the Buy Free Spins feature may also allow players to purchase direct access to their preferred free spins option.

The Dog House Megaways combines a lighthearted canine theme with multiplier wilds and two distinct free spins features.

3. San Quentin Slot

… (content continues unchanged) …

FAQ: Bonus Slots