Nightblood, Curse Sword

As an additional cost to cast this card, gain X poison counters.
If creature that equips this artifact attacks, all
non-invested creatures that defend are exiled,
and creatures that equip this artifact ignore all keywords when attacking, unless the opposing creature is invested. When attacking invested creatures, remove invested and then place
2 -X/-X counters on them. After a creature that
has equipped this artifact attacks, it is sacrificed,
and this artifact returns to your library.