Reel Engine
Megaways™
Megaways™ is a dynamic reel modifier patented by Big Time Gaming (BTG) in 2016. Unlike fixed-reel games where each column displays the same number of symbols every spin, a Megaways engine randomises the height of each reel on every spin, generating a different number of visible symbols per column — typically between 2 and 7.
The maximum ways-to-win is calculated by multiplying the number of visible symbols per reel across all active reels. On a standard 6-reel Megaways game with a maximum of 7 symbols per reel, the maximum is 7⁶ = 117,649 ways.
BTG licenses the Megaways™ engine to other developers. Licensed titles include games from Pragmatic Play, Red Tiger, Blueprint Gaming, and many others. The original Bonanza Megaways (2016) established the template that hundreds of subsequent games followed.
Key Characteristics
Patent holder: Big Time Gaming (AU)
First game: Dragon Born (2016)
Max ways: 117,649 (6 reels × 7 symbols)
Typical volatility: High to Very High
Payline Alternative
Cluster Pays
Cluster Pays replaces the traditional payline model with a proximity-based win detection system. Rather than requiring symbols to land on a specific left-to-right line, Cluster Pays awards wins when a defined minimum number of identical symbols appear in an adjacent grouping — horizontally, vertically, or both — anywhere on the grid.
The standard cluster threshold is 5 adjacent symbols of the same type. Larger clusters award higher payouts on a sliding multiplier scale. This system is typically implemented on a 7×7, 8×8, or similar square grid rather than the rectangular grids used in payline games.
NetEnt's Aloha! Cluster Pays (2016) brought the mechanic to mainstream attention, though earlier implementations existed in casual game design. The cluster model pairs naturally with cascading/avalanche mechanics and sticky wilds.
Reel Animation
Avalanche / Cascading Reels
The Avalanche mechanic — also marketed as Cascading Reels, Tumbling Reels, or Rolling Reels depending on the provider — removes winning symbols from the grid after a win and allows new symbols to fall (or burst, or roll) into the vacated spaces from above. This creates the possibility of chain-reaction wins from a single paid spin.
NetEnt's Gonzo's Quest (2011) popularised the mechanic under the "Avalanche" name. Symbols fall down from above after a win, and each consecutive cascade in the same spin adds a multiplier tier to all subsequent wins. This multiplier chain is a defining secondary feature of the mechanic in many implementations.
The mathematical effect is significant: a single spin that triggers three cascades at 1×, 2×, 3× multipliers effectively yields the sum of three separate win events, amplified progressively. High-cascade sequences are responsible for the largest single-spin wins in Avalanche-based games.
Cascade Multiplier Example (Gonzo's Quest)
| Cascade # | Base Game Mult. | Free Fall Mult. |
|---|---|---|
| 1st win | 1× | 3× |
| 2nd cascade | 2× | 6× |
| 3rd cascade | 3× | 9× |
| 4th cascade+ | 5× | 15× |
Symbol Modifier
Wild Symbol Variants
The Wild symbol is the most widely used modifier in slot design. In its base form, a Wild substitutes for any standard paying symbol to complete a winning combination. Over decades of game development, designers have created dozens of Wild variants, each altering the grid in distinct ways.
Sticky Wilds
A Wild that remains in its position for one or more subsequent spins after landing. During Free Spins rounds, Sticky Wilds accumulate over the bonus, creating a progressively wilder grid as the feature continues. They reset when the bonus ends.
Expanding Wilds
When an Expanding Wild lands, it expands to cover an entire reel column (vertically) or row (horizontally). This dramatically increases the surface area covered by the Wild and can create multi-line wins from a single symbol landing.
Walking / Shifting Wilds
A Wild that moves one position (typically left) on each subsequent free spin. This guarantees multiple win-line evaluations from a single Wild across several spins, making Walking Wilds especially valuable early in a free spins bonus.
Multiplier Wilds
A Wild carrying a multiplier value (2×, 3×, 5× etc.) that applies to any win it helps complete. When two Multiplier Wilds contribute to the same win, their values are typically multiplied together (e.g., 3× × 3× = 9× total win).
Stacked Wilds
Wilds that occupy multiple vertical positions on a reel simultaneously (as a "stack" of 2, 3, or 4+ Wild symbols). When a full-reel stack lands, it creates the same effect as an Expanding Wild while operating within the standard symbol draw.
Colossal / Mega Wilds
An oversized Wild symbol occupying a 2×2, 3×3, or larger block on the grid simultaneously. Popularised by WMS Gaming's Colossal Reels format, these create massive grid coverage from a single symbol event.
Bonus Round
Hold & Win / Lock & Spin
Hold & Win (also known as Lock & Spin, Respin, or Cash Collect depending on the provider) is a bonus round mechanic where special coin symbols land on the reels and "lock" in place. A respin cycle of 3 begins, and any additional coins that land reset the counter to 3. The round ends when the counter reaches 0 or the grid is filled.
Coin symbols carry printed cash values (ranging from tiny fractions of the bet to thousands of times the bet). Special jackpot positions (Mini, Minor, Major, Grand/Mega) may also appear and award fixed jackpot amounts regardless of coin density.
The mechanic was first widely deployed in the slots market by Playson and Blueprint Gaming around 2018–2019, and subsequently adopted by virtually every major slot developer. Its appeal lies in the clearly visible accumulation mechanic — players can see their total growing with each coin lock.
Reel Engine
Infinity Reels™
Infinity Reels™ is a patented mechanic developed by ReelPlay (licensed through Yggdrasil's YGS Masters programme) in which the reel grid can expand indefinitely during a single spin sequence. The game begins with a 3×3 or 4×3 grid. If a win occurs, a new reel column is added to the right side and the win is re-evaluated. This continues for as long as wins occur — theoretically without limit.
Each time a reel is added, a progressive multiplier also increases (typically +1× per expansion). This means an Infinity Reels chain that extends to 10 reels carries a 10× multiplier on the final win. The combination of expanded ways and growing multiplier makes Infinity Reels sequences capable of extreme payouts.
The mechanic is theoretically uncapped in expansion but practically limited by the mathematical probability of consecutive wins across an ever-growing ways calculation. Published titles include Barbarian Fury, Odin Infinity Reels, and Egyptian Infinity Reels.
Infinity Reels Expansion Example
| Reel Count | Ways (3 rows) | Multiplier |
|---|---|---|
| 4 (start) | 81 | 1× |
| 5 | 243 | 2× |
| 6 | 729 | 3× |
| 7 | 2,187 | 4× |
| 8 | 6,561 | 5× |
| 10+ | 59,049+ | 7×+ |
Pay Structure
All-Ways Pay (243 / 1024 Ways)
All-Ways Pay removes the concept of fixed paylines entirely. A win is awarded whenever matching symbols appear on consecutive reels from left to right, regardless of their row position. On a standard 5×3 grid, this produces 3 × 3 × 3 × 3 × 3 = 243 possible win positions — hence "243 Ways." On a 5×4 grid: 4⁵ = 1,024 Ways.
Unlike Megaways (which is dynamic per spin), All-Ways Pay grids have a fixed ways count. The ways figure simply represents the total count of possible symbol position combinations across all reels. Microgaming's Thunderstruck II (2010) popularised the 243-ways format, which remains one of the most common pay structures in the industry.
Symbol Removal
Tumble / Rolling Reels
Tumble (Pragmatic Play's term) and Rolling Reels (Microgaming's term) are cascade mechanic variants. Functionally identical to Avalanche, the distinction is primarily visual and branding-based: Tumble symbols "tumble" away from the grid on win; Rolling Reels symbols "roll" off the bottom. New symbols enter from the top in both cases.
Some Tumble implementations add specific multiplier trails or progressive win counters not found in all Avalanche variants. Pragmatic Play's Gates of Olympus uses a Tumble mechanic where multipliers appear randomly during the spin and apply to all wins on that tumble sequence — a distinct mathematical structure from cascade multipliers that increase per chain step.