The Stationary Knight of Play

Flash, Defender, Indestructible
This card enters the battlefield with five -1/-1 counters on it.
At the beginning of your upkeep, for each
artifact that you don't control, put a -1/-1
counter on this card.
{p/b}{p/b}: remove two -1/-1 counters from this card,
each player discards their hand.