Is Slithering Cryptid legal in Standard, Modern, and Commander?

Slithering Cryptid is legal in: Standard, Modern, Pioneer, Legacy, Vintage, Commander, Pauper, Historic.

Slithering Cryptid

Q: What type of card is Slithering Cryptid?

Slithering Cryptid is a Creature — Fish Mutant. Its oracle text reads: "When this creature enters, create a Mutagen token. (It's an artifact with "{1}, {T}, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")"

Creature — Fish Mutant

When this creature enters, create a Mutagen token. (It's an artifact with ", , Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")