Plinko
A ball falls through rows of pegs, bouncing left or right, and lands in a bottom slot that sets your multiplier.
Plinko borrows its board from a TV game show. A ball tumbles through a triangle of pegs and settles in one of the slots along the bottom. Slots near the centre pay modest multipliers; the outer ones pay big.
Turning seeds into bounces
A typical provably fair version spends one float per row. Under 0.5 the ball goes left, 0.5 and up it goes right, though each casino sets its own rule. A 16-row board therefore needs 16 floats, more than a single 32-byte HMAC output supplies, so the game moves on to the next HMAC round via the cursor.
Rows and risk
Changing the row count or the risk setting changes the payout table and the variance. More rows and higher risk bring bigger top multipliers along with more frequent small losses.
Odds on an 8-row board
The count of right-hand bounces follows a binomial distribution. Only 1 of the 256 possible paths ends in each outer slot, which is why the edges pay so much. The centre slot is reached by 70 of 256 paths and, on most risk levels, returns less than you staked.