Gruul Beastmaster {3}{G}

Creature — Human Shaman

Riot (This creature enters with your choice of a +1/+1 counter or haste.)

Whenever Gruul Beastmaster attacks, another target creature you control gets +X/+0 until end of turn, where X is Gruul Beastmaster’s power.

2/2

Watermark: Gruul

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Prints	USD	EUR	TIX
Ravnica Allegiance	$0.03	€0.06	0.05

The value of X is determined only as Gruul Beastmaster’s triggered ability resolves. Once that happens, the value of X won’t change later in the turn even if Gruul Beastmaster’s power changes. (2019-01-25)
If Gruul Beastmaster leaves the battlefield before its triggered ability resolves, use its power as it last existed on the battlefield to determine the value of X. (2019-01-25)
If Gruul Beastmaster’s power is negative as its triggered ability resolves, X is considered to be 0. In other words, that ability can’t cause the creature to lose power. (2019-01-25)

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. (2019-01-25)
If a creature entering the battlefield has riot but can’t have a +1/+1 counter put onto it, it gains haste. (2019-01-25)
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. (2019-01-25)