The Siren of the Deep

Lifelink, islandwalk, swampwalk.

Ward — Sacrifice a non-basic land.

When The Siren of the Deep enters the battlefield,
each player mills X cards from their library, where
X is the amount of non-basic lands they control.
While The Siren of the Deep is on the battlefield,
you may cast spells milled this way from target graveyard using mana of any color to cast them.