Is Sealock Monster legal in Standard, Modern, and Commander?

Sealock Monster is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

Sealock Monster

Q: What type of card is Sealock Monster?

Sealock Monster is a Creature — Octopus. Its oracle text reads: "This creature can't attack unless defending player controls an Island. {5}{U}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.) When this creature becomes monstrous, target land becomes an Island in addition to its other types. Power/Toughness: 5/5"