Crash is not profitable over time, whatever system a player follows. Every multiplier carries the same built in edge, usually one to five percent, so cashing out early wins often but small, and waiting for large multipliers wins rarely. Anyone asking how to win at crash is really asking how to lose slowly: a fixed cash out point and a fixed budget keep a session short, but they cannot put the house edge on the player's side.
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 overcomes the edge.
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 where they live.