Joo'n, the Fearless Climber

Whenever one or more creatures you control
attack, reveal the top card of your library. If that
card's a creature card, put it onto the battlefield
tapped and attacking a defending player or a
planeswalker they control. If it's not, put it into
your graveyard. If you put that card onto the
battlefield this way, shuffle it into your library at
end of combat.
Partner (You may have two commanders if
both have partner.)