Is Nightkin Ambusher legal in Standard, Modern, and Commander?

Nightkin Ambusher is legal in: Legacy, Vintage, Commander.

What type of card is Nightkin Ambusher?

Nightkin Ambusher is a Creature — Mutant Warrior. Its oracle text reads: "Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.) When this creature enters, target player gets four rad counters. This creature can't be blocked as long as defending player has a rad counter. Power/Toughness: 4/4"