Chibeasties Slot by Yggdrasil Gaming

Forget the math for a second and look at the reels: pudgy purple onion-monsters, a curled-up blue snail, a spiky orange hedgehog, all glaring with anime-sized eyes from inside woody green roundels. The whole thing sits between two chunky tree trunks with a mossy floor underneath, like someone pasted Saturday-morning cartoon characters into a children's storybook. Yggdrasil released this back in 2015, and it shows in the simplicity of the base game. There's no ante bet, no wheel, no collection meter, nothing layered on top of the line wins. You spin, you land 3 of a kind on one of the 20 lines, you get paid. That's it for the base.

The whole pull of the game is what happens when you trigger Free Spins. Three scatters award 10 spins, four gives you 20, five lands the full 40. There's no retrigger because the scatter symbol disappears entirely once the bonus starts, so whatever you trigger with is what you get. At the start of every free spin round, the game randomly picks one symbol out of the 8 regular beasties plus the Wild and flags it as the Expanding Symbol for that round. Whenever that chosen symbol drops onto the reels, it stretches to fill the entire reel it landed on.

The clever bit is the double-pay rule. Line wins are calculated first with the symbol in its normal one-position state, then again after it expands. If a line had a winning combo before expansion AND the expansion creates wins of its own, that line pays twice on the same spin. So a 5-of-a-kind hit on a payline containing the chosen symbol effectively pays double. The Wild substitutes for any regular in the usual way, but it only expands if it was the symbol picked at the start of the round. If a low-pay symbol gets chosen, the round will be quiet. If the top beastie gets the nod, you're suddenly in 2,000x territory.

It's a single-mechanic slot, dressed up in cartoon art, and the whole 40-spin scenario is what you're actually chasing.