Is Hydra Trainer legal in Standard, Modern, and Commander?

Hydra Trainer is legal in: Modern, Legacy, Vintage, Commander, Historic.

Hydra Trainer

Q: What type of card is Hydra Trainer?

Hydra Trainer is a Creature — Human Warrior. Its oracle text reads: "You may exert this creature as it attacks. When you do, target creature gets +X/+X until end of turn, where X is the number of counters on permanents you control. (An exerted creature won't untap during your next untap step.) {2}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)"

Creature — Human Warrior

You may exert this creature as it attacks. When you do, target creature gets +X/+X until end of turn, where X is the number of counters on permanents you control. (An exerted creature won't untap during your next untap step.)

: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)