I'd have to say plain old Living Tar, because I've not gotten far enough in TCB to encounter Gel yet (have been working through the last few levels of JtRH, and designing my own. Didn't find the mudstuff in JtRH too bad)
But just think though - there's still plenty of other tar-like variants that can be created...
e.g. one I thought up just now - the Conscious Slime. Can be destroyed on either an edge or a corner... but only with a direct sword hit (the type that would break a mirror), swipes don't work. The babies would be evil... for they would act like roaches do when there is a brain in the room. After all, it's *conscious* slime
(oooh... I like this. *posts idea to main Feature Requests*)
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