What's your single favorite D&D creature?

[Arkham]

Rakshasa.
Pure evil, conniving, sneaky, brilliant, immune to almost
everything my PCs have, and people are food.

 

[Warrior Psychic]

Githyanki. Most definately ... they have always struck me as a poignant sorta villain. Their magical and psionic power was very stylish. Plus, they just look really cool. Especially since 3rd edition makeover.

I still don't get their -2 Wisdom modifier, though. They seem like natural Psychic Warriors ... until you look at their stats.