Ulug is, of course, a gotcha monster. There are a lot of ways around him; through is the only one that's a really bad idea.

I introduced him with an NPC plain telling the party about the curse. This went basically like this:

NPC: Oh, this is Ulug, he is nasty, he will want whatever you treasure most. My pal Zuk killed him once, Zuk died screaming a few days later, and now Ulug is back.
Party: Sounds bad. Any idea to avoid him?
Druid: Maybe we could banish him?
Cleric: Yup, can do.
Paladin: What does my Divine Sense tell me? (Ulug reeks of evil.) Bleargh, I smite him with my sword!

That was one session ago, now they are desperately trying to figure out how to cure a cursed paladin.

Ulug is humanoid, a little smaller than the average human. He wears a dark coat and a deep hood that obscure his features even to magical light; the only part of his body one may occasionally glimpse is a black-taloned hand.

In (5e D&D) game terms, Ulug is AC 11, has 2 hit points, no attacks and fails all his saves. All of his other stats are average (10, +0 or whatever).

Whoever kills Ulug gets cursed. At the end of each long rest, they have to make two saves:

• Wisdom, DC 15, or lose 1d6 points of Wisdom;
• Constitution, DC 15, or gain a level of exhaustion.

At 0 Wisdom, the cursed character is treated as under a permanent Confusion spell. The levels of exhaustion gained because of the curse cannot be eliminated naturally by rest.

A Remove Curse gives advantage to the next pair of saving throws. A Greater Restoration can either work as a Remove Curse or reduce exhaustion by one level.

The curse itself can only be removed by a Wish.