What it does
Riot lets a creature enter the battlefield with your choice of either a +1/+1 counter or haste. You decide as the creature enters—it's not a static ability you can change later, and you pick fresh each time the creature enters, so a blinked or reanimated Riot creature gets a new choice.
The most common misunderstanding is thinking you get both, or that haste is permanent. You get exactly one: the counter sticks around, but the haste only matters the turn it enters (after that, the creature could attack anyway). Note that haste granted this way is just a one-time benefit baked into the replacement effect, not an ongoing ability.
In Commander, Riot is flexible value. Pick haste when you want immediate pressure or a quick attack with a key creature; pick the counter when the board is stalled and you'd rather bank permanent stats. Blink and recursion effects squeeze extra mileage out of the choice.












