ToME: the Tales of Maj'Eyal

I've gotten the Walrog and Khulmanar, General of Urh'Rok demon seeds and was wondering what other unique demon seeds were out there. Is the only benefit to all of them that you can summon the relevant demon, or do some of them special effects?

IIRC they're not supposed to actually exist. None of them have special effects, just summons. Makes for a pretty shitty slot take up.