Artorias, the Abysswalker

Whenever Artorias, the Abysswalker attacks, you
may sacrifice an undead creature you control. If
you do, he gains your choice of: two +1/+1
counters, first strike, swampwalk, lifelink,
or deathtouch.
Artorias, the Abysswalker does not count as
legendary when resolving abilities of Gwyn,
Lord of Sunlight.