Let's see.
So we can try to hunt down the parasite for good, taking advantage of it being wounded.
If we succeed, then that's it. And sealing the breach should be pretty simple.
But if we fail, the parasite will have had ample time to pull underworld's resources, so the final battle will be at i's toughest. The sealing itself may become compromised.
On the other hand, if try to directly seal the breach, the parasite will notice and rush to stop us.
It will start pulling and concentrating resources, but it will still be hurt and without time to accumulate too much.
So, a middle stage of difficulty
With the breach sealed and the Piper's help, defeating the parasite will be no longer a problem.
We may even have a decent chance of capturing it, facilitating the study of underworld's creatures.
So I'm going for that.
[X] Perform the sealing first, without the connection to the underworld ecosystem, the parasite will not be a threat.