Legendary Creature — Dragon Noble
Flying
Whenever Korvold enters or attacks, sacrifice another permanent.
Whenever you sacrifice a permanent, put a +1/+1 counter on Korvold and draw a card.
4/4
Wyrm hasn't broken down this card yet — check back soon.
Wyrm hasn't mapped related cards for this one yet — check back soon.
→ Infinite card draw, Near-infinite colorless mana, Near-infinite ETB
→ Infinite card draw, Near-infinite ETB, Infinite draw triggers
→ Infinite card draw, Infinite draw triggers, Near-infinite death triggers
→ Near-infinite damage, Infinite card draw, Near-infinite ETB
→ Infinite +1/+1 counters on a creature, Infinite death triggers, Infinite draw triggers
→ Infinite +1/+1 counters on a creature, Infinite damage, Infinite death triggers
If you somehow control no other permanents, you can attack with Korvold. You won't sacrifice anything, and there's no penalty for being unable to do so.
A legendary permanent that is put into a graveyard because of the "legend rule" isn't sacrificed.
Korvold's last ability is a triggered ability, not an activated ability. It doesn't allow you to sacrifice a permanent whenever you want; rather, you need some other way of sacrificing permanents, such as Korvold's first triggered ability.
If you sacrifice a permanent as part of a spell or activated ability's cost, Korvold's last ability will resolve before that spell or ability.
If you sacrifice Korvold, its last ability triggers. You won't put a +1/+1 counter on anything, but you'll draw a card.