Thunder Coins XXL: Booster Cells Slot Review

Playson's Thunder Coins line has been picking up gold coins the same way for five games now, and this fifth one finally gives the board a memory. Thunder Coins XXL: BoosterCells is a 3x5 machine with 15 fixed paylines, arriving first as a Starcasino exclusive in Belgium on 17 September 2026 before going anywhere else. The RTP sits at 95.65% and the ceiling is 12,000x the bet. The real draw is the Bonus Game, where every collected coin leaves its value printed on the cell it landed in, ready for the next coin to pick up and carry.

The reels are set up like an old-fashioned fruit machine. The symbols include cherries, oranges, plums, lemons, blue grapes, sliced watermelon, golden bells, a BAR BAR plate, and a red 777 on top. Because it uses a three-reel grid, there is exactly one winning length in the whole game: three of a kind or nothing. The 777 doubles as the wild and as the best symbol at 30x the bet, while bells pay 10x and BAR pays 8x. The fruit symbols slide all the way down to half your stake, which tells you straight away that the base line hits are not where the money is.

Sitting on top of the lines is a second pay system that ignores them completely. Gold coins land with cash values stamped on their faces, anywhere from 1x to 8x the total bet. A coin is worth precisely nothing until a blue Thunder Coin turns up on the same board. When one does, the Thunder Feature fires and sweeps up every coin showing, adding the lot to the win. Without that collector, the coins are just wallpaper. You can land a screen full of high values and jackpot coins, and the spin will still pay zero.

The wild cannot rescue a dead screen either. The 777 substitutes for everything except the coins and the Thunder Coins, so there is no back door into a collect. That one exclusion keeps the feature scarce, which makes the base game very quiet for long stretches. A full grid of one symbol is usually how the line game produces anything noticeable at all.

Landing enough coins and Thunder Coins on a single board opens the Bonus Game. There is also a random helper called the Pile of Gold Feature that can trigger on any coin landing during the base game. When it fires, it drops in enough extra coins or Thunder Coins to trigger the bonus outright, though it acts more like a happy accident than a reliable route in.

The route you can actually control sits in the red panel beside the reels. Double Chance costs 1.5x the total bet and doubles the chance of triggering the bonus. Thunder Spin costs 4x the bet and guarantees one Thunder Coin on every spin. That is a bigger change than it sounds, because having a collector on the board every single time means every coin that lands gets paid. At four times the stake, it certainly needs to be.

Underneath, the bonus is a hold-and-win that behaves mostly the way you would expect. You get three respins that reset each time a new symbol lands, and the round is over when the counter empties. The board swaps to its own short reel strips for the duration, and nothing actually reaches your balance until the round officially closes.

The BoosterCells mechanic is the only genuinely new idea here, and it changes how the whole round builds. Every collected coin leaves its value stored on the cell where it landed, marked as a pale plus figure. If a later coin drops onto that cell, it absorbs the stored number, and the coin's new total becomes the new stored value for that position. Whenever a Thunder Coin lands, it randomly boosts several stored values at once. The round compounds instead of just accumulating, turning small opening coins into heavy values by the end.

The restriction that makes the mechanic work is also what ruins it. Thunder Coins land on reel 2 and nowhere else, and they stick there for the rest of the round. Everything that gets collected drains into that middle strip. Reels 1 and 3 store their values beautifully and then just sit there being interesting, leaving huge multipliers stranded on the board.

One practical warning for the bonus is that the respins are entirely manual. A long round is a long sequence of button presses rather than something you can just sit back and watch, complete with a starting card that waits indefinitely for you to click to continue.

The game offers two bonus purchases, priced at 75x and 200x the total bet. The cheaper option is the ordinary Bonus Game, while the 200x Super version guarantees three Thunder Coins stacked down reel 2 on the opening board. The pricing is a straight multiple all the way up the stake ladder, so there is no volume discount hiding at either end.

Both versions of the bonus are capable of running long and filling up the board nicely, but they also expose the frustrating geometry of the game. A round can easily stretch to sixteen or seventeen respins, building up massive stored values on the outer reels. Because no Thunder Coin can land on reels 1 or 3, all those heavy numbers are just left standing there uncollected when the respins run out. The payout comes entirely from the middle strip.

Four jackpot plates run along the top of the screen: Mini, Minor, Major and Grand, worth 15x, 30x, 100x and 1,000x the total bet. They are fixed multiples rather than progressives, so they scale perfectly with the stake. A jackpot here is not a separate event with its own trigger, but simply a coin face that lands like any other. It is collected by the same Thunder Feature, which means a Grand coin is worth absolutely nothing if no Thunder Coin joins it on the board.

The ceiling is 12,000x the bet, and since the Grand jackpot is only 1,000x, the biggest single coin in the game is just a twelfth of the maximum. Nothing hands out 12,000x in one piece. It has to be assembled out of a bonus round where the cells have been boosted for a very long time and reel 2 keeps sweeping the board. Playson estimates that happens roughly once in fifty billion spins. Most of the studio's boards reach higher than this one does, with games like Golden Penny x1000: Super Wheel topping out at 20,000x against this game's 12,000x.

The artwork takes one loud idea and fully commits to it. Classic fruit symbols sit on a deep blue field with white lightning forking behind the reels, joined by gold-rimmed coins and chrome-blue lettering. It dresses up the oldest symbol set in slots to read as modern rather than nostalgic, and it holds up well over time. The bonus board is the better-looking half, going dark navy so the stored values glow as pale ghosts on their cells. It is a genuinely useful touch that lets you see exactly which parts of the board are loaded at a glance.

So much of this game lives inside the BoosterCells mechanic, and very little lives outside it. The base game is a quiet three-reel fruit machine with a low top symbol and long dead stretches, heavily reliant on a collector symbol to make its coins worth anything. The bonus is a completely different story, offering a compounding board that is properly satisfying to watch fill up. What spoils the experience is the strict geometry. Reel 2 does every bit of the collecting while the outer reels turn into a column of numbers you get to admire and never touch. Anyone who has ground through Playson's coin rounds and wished the board would remember something between respins now has exactly that, even if it can be frustrating to watch the best numbers get left behind.