Is Cateran Slaver legal in Standard, Modern, and Commander?

Cateran Slaver is legal in: Legacy, Vintage, Commander.

What type of card is Cateran Slaver?

Cateran Slaver is a Creature — Horror Mercenary. Its oracle text reads: "Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.) {5}, {T}: Search your library for a Mercenary permanent card with mana value 5 or less, put it onto the battlefield, then shuffle."