Perhaps a scaling challenge with difficulty based on how many weasels you have?
Pulling it off costs the whole bunch, but either greatly reduces wounds or outright clears it. And each time you do, it requires increasingly absurd numbers of weasels to ensure reasonable chances of succeeding.
(Boatman’s caught offguard the first time, thought you wouldn’t do it a second, and prepared for you to try it again on the third.)
And if you fail, it gives wounds and takes a bunch of your weasels.