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Okay, I suggest three options:
1) Rush to the boss along the shortest path, possibly avoiding particularly large groups of rats.
2) Lure everyone out of the collector with a drum, positioning yourself outside the exit. Kill them one by one (or as many as can fit through the door at once). Then, switch to option 1 or 3.
3) Wander around, intentionally searching for and killing everyone. But the rats have 350 HP, keep that in mind... Dodge isn't super high, but I wouldn't want to spend all my ability slots on them without even reaching the boss.
With option 3, and possibly with option 1 as well, it would be good to barricade the exit so that no one can escape into the town.
I'm in favor of option 1, and yes, probably with a barricade.
Let Arandor decide 🙃