Is Mikaeus, the Lunarch legal in Standard, Modern, and Commander?

Mikaeus, the Lunarch is legal in: Modern, Legacy, Vintage, Commander, Historic.

What type of card is Mikaeus, the Lunarch?

Mikaeus, the Lunarch is a Legendary Creature — Human Cleric. Its oracle text reads: "Mikaeus enters with X +1/+1 counters on it. {T}: Put a +1/+1 counter on Mikaeus. {T}, Remove a +1/+1 counter from Mikaeus: Put a +1/+1 counter on each other creature you control."