Mines is a gambling game played on a grid with hidden bombs. A player chooses how many mines to place, then uncovers tiles one by one; each safe tile raises the payout, and hitting a mine ends the round. The dice game on these sites is simpler still: a player picks a target number and wins if a random roll lands above or below it. Both are legit when the results can be verified, and neither has a way to win that beats the edge.
Plinko is a game in which a ball drops through rows of pegs and lands in a slot along the bottom, each slot paying a fixed multiple. It borrows the board from a television prize game and looks like pachinko, but the two are not the same: pachinko is a machine game of its own, while online plinko boards are drawn on screen. The payout table does not change during the drop, and the random result picks the slot.
Plinko odds depend on how many rows the board has and which risk level a player picks; more rows and higher risk widen the gap between the rare edge slots and the common middle ones. Whether plinko is rigged or legit comes down to the site: a licensed game with provably fair results can be checked, an unlicensed one cannot. Plinko for real money makes money for the casino through its edge, and a free demo lets anyone play plinko without money, subject to the legal age in their country.