Aboleth 24
Adult/Ancient Chromatic (Evil) Dragon 22
Adult/Ancient Metallic (Good) Dragon 7
Beholder 26
Death Tyrant 22
Demilich 26
Dracolich 22
Elder Brain 23
Gynosphinx 1 + 1 = 2 I don't know if this is a good monster or not, I don't want anybody to waste their second downvote when they kill it.
Ki-rin 4
Kraken 23
Lich 29
Mummy Lord 20
Unicorn 13
Vampire 22 - 2 = 20
Inspired by Final Fantasy (and with apologies to The Phantom of the Opera): Hero sings "Magical LightAxe, my companion! Bringing illumination..." Vampire interrupts "...boiling the blood in my veins!"