Brutus: Timiring is only vulnerable when confronted with its own worst fear, otherwise it's pretty much unkillable. Astrid: And that fear would be what? Brutus: Huh? Um... it's not specified, unfortunately.
Lilly: Why are you so invested in helping us close the portal? Brutus: Fair enough. TLDR: I come from a long line of interdimensional monster-hunter mentors as part of an organization called the portal protectorate. Agents are trained from hatchlings to monitor the border between worlds and to step in if there's a breach. It's all very official. We even have badges!