Is Realm Seekers legal in Standard, Modern, and Commander?

Realm Seekers is legal in: Legacy, Vintage, Commander, Historic.

What type of card is Realm Seekers?

Realm Seekers is a Creature — Elf Scout. Its oracle text reads: "This creature enters with X +1/+1 counters on it, where X is the total number of cards in all players' hands. {2}{G}, Remove a +1/+1 counter from this creature: Search your library for a land card, reveal it, put it into your hand, then shuffle."