Slot Features & Mechanics, Explained
This is our library of slot features and mechanics — what each one actually does, where it came from, and which games use it best. Every guide below breaks one mechanic down in plain English, with verified figures and links to the full family guide for each game we cover.
New guides are added regularly. Pick a mechanic below, or skim the primers further down the page if you’re not sure where to start.
Expanding Wilds Slots: From Starburst to the 5×5 Giants
How the full-reel wild works, from Starburst’s respin-triggering jewels to Push Gaming’s 5×5 giants — the six games that define the mechanic.
Sticky Wilds Slots: Seven Games Where the Wilds Refuse to Leave
Wilds that lock in place for the whole feature: the seven sticky wilds slots that matter, from Dead or Alive’s line-up chases to Wild Swarm’s hive.
Free Spins Slots: A Field Guide to Every Bonus Variant
Mode-picks, unlockable chambers, multiplier ladders, collect upgrades: the five free spins variants explained through the 12 games that define them.
Bonus Buy Slots UK: Why You Can’t Buy the Feature Here
Why the buy button is missing from every GB-licensed slot: the Gambling Commission rules behind the feature-buy ban, and the January 2026 bonus changes.
Progressive Jackpot Slots: Networked, Local and Must-Drop, Untangled
Networked, local, must-drop or tiered — the jackpot types explained properly, with the games that define each one, from Mega Moolah to Dream Drop.
Scatter Pays Slots: The Games That Killed the Payline
No paylines, no ways: how scatter pays slots count 8+ symbols anywhere, and the Pragmatic, Nolimit and Relax games that define the pay anywhere format.
Cascading Reels Slots: Why One Spin Can Keep On Paying
Tumble, Avalanche or Tumbling Reels — how cascading slots chain wins from a single spin, and the 12 games from Gonzo’s Quest to Gates of Olympus that define it.
Cluster Pays Slots: How Grids Beat Paylines
What counts as a cluster, how NetEnt’s Aloha! named the mechanic, and the 15 grid slots from Reactoonz to Sugar Rush that define cluster pays.
Hold and Win Slots: One Mechanic, a Dozen Names
How hold and win slots work — locked symbols, resetting respins, grid-fill jackpots — and the 21 games that define the format, from Lightning Link to Money Train.
Megaways Slots: The Engine That Rewired UK Casinos, Game by Game
Megaways explained and ranked — Bonanza, Extra Chilli, White Rabbit and every licensed build that matters, with the engine mechanics and the €450m story behind it.
What this section covers
Most slot reviews assume you already know what a mechanic means — ours don’t. Each Features guide explains one mechanic or bonus feature from the ground up: how the maths behaves, who invented it, what the different studio trade names mean, and a table of the games built on it. Wherever a game belongs to a family we’ve reviewed in full, the guide links straight through to that series page, so you can go from “what is cluster pays?” to a complete family comparison in two clicks.
The most popular slot mechanics
Four mechanics account for most of what UK players spin today. Hold & Win locks bonus coins in place across three respins and hands out grid-fill jackpots — you’ll see it branded as Hold & Spin, Link & Win or Fire Blaze depending on the studio. Cluster pays throws out paylines entirely and pays for groups of adjacent symbols, the format behind Reactoonz and Jammin’ Jars. Cascading reels remove winning symbols and drop new ones in, chaining wins from a single spin — the engine behind Gonzo’s Quest and every Pragmatic “tumble” hit. And scatter pays goes a step further than clusters: eight-plus matching symbols pay from anywhere on the grid, no adjacency needed.
Popular bonus features
Beyond the core engines sit the features that decide how a bonus round actually plays. Free spins come in more flavours than most players realise — pick-your-volatility modes, unlockable chambers and climbing multiplier ladders all behave very differently. Sticky wilds lock in place for the rest of a feature and power the legendary Dead or Alive line-up chases, while expanding wilds grow to swallow whole reels, Starburst-style. Progressive jackpots pool stakes across networks of games into life-changing pots — and if you’ve ever wondered why you can’t buy the bonus like streamers do, that’s a UK rule, and we explain it.
Popular series built on these mechanics
Some mechanics grew into entire franchises. Megaways is the biggest — a licensed engine that randomises the number of symbols per reel, now inside hundreds of UK slots. Money Train turned the Hold & Win respin into a four-game saga with a 150,000x ceiling, Big Bass Bonanza built the UK’s biggest modern franchise on collect-style free spins, and Sweet Bonanza and Gates of Olympus made tumbling, pay-anywhere grids the default look of a 2020s slot. Every one of them — and dozens more — has a full family guide in our Slot Series index.