I'm very personally a sucker for this. I had a mind flayer that was a recurring "ally" that showed up in my last campaign. The cleric was constantly having an aneurysm about letting him live, but he saved and helped the party multiple times. My favourite npc of the game, just ahead of the mimic the party befriended and then had guard the orphanage during an attack on the city. The kids celebrated it as a hero, so it stayed there, shape-shifting into playground equipment. This too stressed out the cleric. They were briefly friendly with a Beholder, but ultimately weren't able to see eye to eye.Fuck... I love pragmatic characters. I bet he'd ally Hitler too, if it furthered his goals.