Mimir, Keeper of Knowledge

At the beginning of each end step exile the top
card of your library. Cards exiled this way gain
"You may play this card from exile as long as you
control a Mimir, Keeper of Knowledge."
Whenever an opponent cast a spell, that player
may pay {2}. If the player doesn't, you may untap
a tapped land you control.
Partner (You can have two commanders if both have partner.)