Rhythm of the Wild

If Rhythm of the Wild leaves the battlefield at the same time that a nontoken creature enters the battlefield (most likely because that creature has a replacement effect, such as that of Rescuer Sphinx), that creature still gets a +1/+1 counter or haste.

Wotc — May 03, 2019

Once a creature with riot has entered the battlefield, it keeps its +1/+1 counter or haste even if it loses riot.

Wotc — January 25, 2019

If a nontoken, noncreature permanent becomes a creature after it's already on the battlefield, it will have riot but it will be too late for the replacement effect to have any effect.

Wotc — January 25, 2019

A noncreature card that happens to be entering the battlefield as a creature will have riot (for example, Rusted Relic while you control three other artifacts). Similarly, a creature card entering the battlefield as a noncreature permanent won't have riot (for example, Thassa, God of the Sea while your other permanents contribute only four to your devotion to blue).

Wotc — January 25, 2019

A spell or ability that counters spells can still target a creature spell you control. When that spell or ability resolves, the creature spell won't be countered, but any additional effects of that spell or ability will still happen.

Wotc — January 25, 2019

If a creature entering the battlefield has riot but can't have a +1/+1 counter put onto it, it gains haste.

Wotc — January 25, 2019

If you choose for the creature to gain haste, it gains haste indefinitely. It won't lose it as the turn ends or as another player gains control of it.

Wotc — January 25, 2019

If a creature enters the battlefield with two instances of riot, you may choose to have it get two +1/+1 counters, one +1/+1 counter and haste, or two instances of haste. Multiple instances of haste on the same creature are redundant, but we're not going to tell the Gruul how to live their lives.

Wotc — January 25, 2019

Riot is a replacement effect. Players can't respond to your choice of +1/+1 counter or haste, and they can't take actions while the creature is on the battlefield without one or the other.

Wotc — January 25, 2019