The ancient mimir of Sigil

Hexproof. Indestructible.
You may look at, play lands and cast spells from
the top of your opponents' libraries. You may
spend mana as though they were of any color
to cast those spells. Spells cast this way will be
controlled by your opponents on each of their
turns and by you during your turn.
"He knows enough secrets not to be challenged."