Having the Horde awaken once the player makes a certain advancement. This suggestion is mainly for modpack purposes or tying a bit more with other calamity mods in general.

Example: The Horde awakens after the player gets the advancement "We Need to go Deeper" or "Nothing built lasts forever" (from the CWSM mod).

I think this is a good idea, I'll see if there is a way to do this.