Opolis, the City-God

When Opolis or a land enters the battlefield
under your control, exile all lands you control
until Opolis leaves the battlefield.
Opolis gets +1/+1 for each land exiled by it.
Lands you control enter the battlefield tapped if
you controlled a permanent named Opolis, the
City-God at any point this turn.
Once per turn, you may cast a spell without
paying its mana cost if its converted mana cost is
less than or equal to Opolis's power.