So, when I control no monsters or if I control an “Ogdoadic” monster I should be able to special summon “Nunu, the Ogdoadic Remnant” from my GY. But if I control “Ogdoabyss, the Ogdoadic Overlord” Nunu doesn’t see that as an Ogdoadic monster and I can’t use the special summon effect in GY.
There’s no problem with other Ogdoadic cards though. If I tribute Ogdoabyss for another Ogdoadic monster, or there’s other Ogdoadic monsters beside Ogdoabyss, I’m able to use Nunu’s effect no problem. It only happens if I only control Ogdoabyss.