He's watching the gap for all horrors. And only the bigger ones would be powerful to build a bridge over the gap. Smaller ones would "tagalong" across the gap, but they can't bridge it on their own. You need MORE mana for the smaller ones to come across.
Okay, that's doesn't make sense either, otherwise the most powerful would be able to come across now...
Gods, I hate magical theory. Much easier to just tell the mage to blow up the building. Let me work on my theory a bit and I'll get back to you.
Well, they have enough
skill to work with what they've got, reaching into our world on a micro-level and influencing plots to open the way from inside, as illustrated by all those examples in this thread. That's why they're so powerfull. But wvwn they need mana spikes and cults dedicated to their goals to stay.
And as The_Gun_Nut wrote - they could work something out. But with difficulty. That's why metaplot characters managed to spoil their fun for now...
I bet in some time - maybe with the finale of the Dawn of Artifacts series - there will be a Big Bad Horror to beat for the players and their allies.
Now imagine all that power contained in artifacts that remained from the Fourth World used to create a mana spike. That'd be neat for Bone Crown, for example.
This would vary according to the "species" of Horror, and would mean that any that managed to stay during the downcycle (like Yrsgrathe) had to work very hard to maintain themselves in high mana/specialized areas.
As with the Great Dragons, and metahumans, who needed a certain amount of magic to survive. Some Horrors might have devised a way to stay hidden during downtime. But they still would need more magic to wake up.
With some exceptions. Verjigorm, for example. I don't think he even plays by the same rules...