Is Maester Seymour legal in Standard, Modern, and Commander?

Maester Seymour is legal in: Legacy, Vintage, Commander.

Maester Seymour

Q: What type of card is Maester Seymour?

Maester Seymour is a Legendary Creature — Human Elf Cleric. Its oracle text reads: "At the beginning of combat on your turn, put a number of +1/+1 counters equal to Maester Seymour's power on another target creature you control. {3}{G}{G}: Monstrosity X, where X is the number of counters among creatures you control. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)"

Legendary Creature — Human Elf Cleric

At the beginning of combat on your turn, put a number of +1/+1 counters equal to Maester Seymour's power on another target creature you control.

: Monstrosity X, where X is the number of counters among creatures you control. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)