Is Mistform Mutant legal in Standard, Modern, and Commander?

Mistform Mutant is legal in: Legacy, Vintage, Commander.

Mistform Mutant

Q: What type of card is Mistform Mutant?

Mistform Mutant is a Creature — Illusion Mutant. Its oracle text reads: "{1}{U}: Choose a creature type other than Wall. Target creature becomes that type until end of turn. *Familiarity, the first myth of reality: What you know the best, you observe the least.* Power/Toughness: 3/4"