Plinko
Drop a ball through rows of pegs, watch it bounce, and whatever slot it lands in at the bottom sets your payout.
Plinko comes from an old TV game show. You let the ball go at the top, it pinballs down a triangle of pegs, and it settles into a slot along the bottom row. Middle slots pay small multipliers. The edges pay big.
Where the bounces come from
Usually, each row of pegs eats one random float. Under 0.5, the ball heads left; 0.5 or higher, it heads right (each site can set its own rule here). A 16-row board means 16 floats, which is more than a single 32-byte HMAC can give, so the cursor kicks over to the next HMAC round.
Picking your settings
More rows or a higher risk level gives you a different payout table and a wilder ride. You unlock bigger top multipliers, but you also eat more small losses along the way.
Real-life odds
On 8 rows, how many times the ball goes right follows a binomial distribution. Just 1 path in 256 ends up at each far edge, and that's why those slots pay huge. The centre slot catches 70 of the 256 paths, and on most risk settings it gives you back less than your bet.