Aboleth

When Aboleth enters the battlefield, one
opponent of its controller's choice reveals their
hand. Whenever Aboleth deals damage to a creature, that creature gains -1,-1 as long as its controller does not control a blue land.
Enslave {t}—target creature on the battlefield
becomes under your control until the end of your
turn. Then, it goes back to being controlled by its
owner and remains on the battlefield. Use only as
a sorcery.