Royal Mint Megaways Slot by Big Time Gaming

The reaction engine here runs in three places at once, not one. Wins on the six main reels clear and refill from above the way you'd expect, but Big Time Gaming bolts a second reel above and a third below reels 2 through 5, and those extra reels react too, sliding fresh symbols in from the right every time a win pays. Triple Reaction is the name, and it means a single winning drop can keep chaining across the whole board long after a normal Megaways grid would have settled.

The gem symbols do the paying, cut purple, red, blue and green stones set in gold, with purple worth ten times what green and blue return on a full six-reel line. Wilds show up only on those two extra reels, always as full-reel wilds, covering everything but the Mint Scatter. All of it plays out in front of a columned Portland-stone mint building with a carved pediment and steps, pink cherry trees in bloom on either side under a clear sky, the sort of stately backdrop that fits a game literally about minting money.

Four Scatters anywhere award 12 free spins, and every Scatter past the fourth adds another four. The pull inside the round is the multiplier: it opens at x1 and climbs by one after every reaction, with no ceiling, so a long reacting run can push it high. In the free spins the Scatters retreat to the extra reels, where three of them retrigger four more spins.

Then there's the slow-burn collection. Any base spin landing exactly three Scatters banks a Gold Bar. Reach 40 banked bars and an extra Scatter gets glued to every base spin until your next trigger, which arrives as the Heartstopper round, an enhanced free spins mode with an even fiercer unlimited multiplier, and where the biggest wins come from. Land four or more Scatters at once and you jump straight there. If you'd rather not grind the bars, the feature buys in directly, with Feature Drop symbols knocking the price down.