Terror of the Abyssal Depths

When this enchantment enters, you may search your library for a Kraken, Leviathan, Octopus, or Serpent creature card, reveal it, put it into your hand, then shuffle.
Whenever a Kraken, Leviathan, Octopus, or Serpent creature enters under your control, target opponent reveals their hand, you choose a nonland permanent from among them with mana value X or less, where X is the mana value of that creature, exile it.