Caetus, Sea Tyrant of Segovia

Noncreature spells you cast have convoke. (Your creatures can help cast those spells. Each creature you tap while casting a noncreature spell pays for or one mana of that creature's color.)

At the beginning of your end step, untap up to four target creatures.

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)

When this Siege enters, create two 1/1 blue Kraken creature tokens with trample.