Is Gigantoplasm legal in Standard, Modern, and Commander?

Gigantoplasm is legal in: Legacy, Vintage, Commander.

What type of card is Gigantoplasm?

Gigantoplasm is a Creature — Shapeshifter. Its oracle text reads: "You may have this creature enter as a copy of any creature on the battlefield, except it has "{X}: This creature has base power and toughness X/X." *"I appreciate things that exceed expectations." —Mizzix* Power/Toughness: 0/0"