Is Mountain Valley legal in Standard, Modern, and Commander?

Mountain Valley is legal in: Legacy, Vintage, Commander.

What type of card is Mountain Valley?

Mountain Valley is a Land. Its oracle text reads: "Mountain Valley enters tapped.{T}, Sacrifice Mountain Valley: Search your library for a Mountain or Forest card, put it onto the battlefield, then shuffle."

Mountain Valley

Land

Mountain Valley enters tapped.<br>, Sacrifice Mountain Valley: Search your library for a Mountain or Forest card, put it onto the battlefield, then shuffle.