Quest for the Holy Grail

Whenever a Knight you control attacks, you may
put a quest counter on Quest for the Holy Grail.
Remove twelve quest counters from Quest for
the Holy Grail and sacrifice it: Create a legendary colorless artifact token named Holy Grail with
"{t}: Target legendary creature you control gains protection from everything until end of turn"
and "At the beginning of your upkeep, if you
control three or more legendary Knights, you
win the game."