Is Horizon Seeker legal in Standard, Modern, and Commander?

Horizon Seeker is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper, Historic.

Horizon Seeker

Q: What type of card is Horizon Seeker?

Horizon Seeker is a Creature — Human Warrior. Its oracle text reads: "Boast — {1}{G}: Search your library for a basic land card, reveal it, put it into your hand, then shuffle. (Activate only if this creature attacked this turn and only once each turn.)"

Creature — Human Warrior

Boast — : Search your library for a basic land card, reveal it, put it into your hand, then shuffle. (Activate only if this creature attacked this turn and only once each turn.)