Frivira, Roil Thief

Landfall - Whenever a land enters the battlefield
under your control, reveal the top card of your
library. If it's a blue spell, cast it without paying
it's mana cost. Otherwise, put it on the bottom of
your library. Frivira, Roil Thief can't be blocked
until end of turn.
Partner (You can have two commanders if both have partner.)