So, my new PG decided to go for MoR, and though in the most of the quests there isn't much choice, I wonder, what would be the thematic choices among monster groups for it?

Expansion-wise, I have all small/big boxes (including MoB), Crusade of the Forgotten, and Treaty of Champions.

I don't mind loosing at all.

Barghests (deag guard dogs), Crow Hags (inhabitants of the mansion), Ironbound (armor suits in the hallways) immediately come to mind.

I guess other humanoids like Dark Priests or Sorcerers might fit as well.

Zombies (former inhabitants/servants of the manor), Rat Swarm (pulsing waves of nasty vermin flowing out from beneath the basement), Razorwings/Harpies (flying around the outside of the cursed mansion) seem like a good thematic fit as well.