Caleb, Vengeful Spectromancer

When Caleb, Vengeful Spectromancer enters the battlefield, exile up to five target creature cards
in opponents graveyards and put a capture counter on each of them.
{u}{b}: Put a creature from exile with a capture counter onto the battlefield under your control.
It is a blue Spirit in addition to its other colors
and types. Activate this ability only any time you could cast a sorcery.