Angel of a Knights Last Valor

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