Noxious Necromancer

Whenever Noxious Necromancer or another
Necron enters the battlefield under your control,
all non- Necron creatures get -1/-1 until end
of turn.
{p/g}{p/g},{t}, Sacrifice another Necron creature:
Destroy target creature with mana value less
than or equal to the sacrificed creature's mana
value. If you paid life to activate this ability
discard a card.