Korvold, Fae-Cursed King

Flying
Whenever Korvold, Fae-Cursed King enters or attacks, sacrifice another permanent.
Whenever you sacrifice a permanent, put a +1/+1 counter on Korvold and draw a card.

Secret Lair Drop

Becoming a dragon only sharpened his raw ambitions.

Year of the Dragon 2024

Transformed at his own wedding, he promptly ate the banquet, the gifts, and the guests.

The List

Throne of Eldraine

A legendary permanent that is put into a graveyard because of the “legend rule” isn't sacrificed.

If you sacrifice Korvold, its last ability triggers. You won't put a +1/+1 counter on anything, but you'll draw a card.

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 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.

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.