Alex, Angel of the Last Valor

Flying, vigilance, haste
When this creature attacks, you may pay
{x}{p/r} to look through your graveyard for
any number of knights with a converted mana
cost of X or less, you may put those cards onto
the battlefield tapped and attacking. The card
return to the graveyard at the end of the next
turn.
"A final valiant effort for something greater
than oneself."