I like the unstoppable cosmic eldritch abomination. The absolute terror and hopelessness. Lets say the only way to defeat something like that is to literally go back and stop its creation. Or somehow protect your galaxy from them ever finding you.... like some big energy barrier? Or thats what godlike entities are there for, or why humanoids ascend to that level, or what Q's involvement was for. Something to cohesively tie things together more. I liked the novelverse with the doomsday machine as an anti borg weapon when i was a kid. And lets say they remove them from ever existing, and then they pop up again from another universe. there were ways to keep that type of force of nature threat going a bit longer. but hindsight is always ... hindsight.