I can't really think of anything at the moment, probably something golem related that's not a lumber would probably be the most effective, but I feel like there should be enemies that could spawn anywhere, with any horde of enemy, that only doesn't resist normal damage (which wouldn't even be doing super effective damage.)
I find that normal weapons have no purpose, especially now with arsenal stations on every floor. You just need to bring the right weapon and you're set.
The only time it's good is when you're fighting Vanaduke, who basically has this concept built into his mask phase.
So why not apply it to a couple of monsters. They don't have to be super common, they can be scarce within waves (like out of 10 enemies 2-3 would be this enemy). That way normal weapons aren't super mandatory. It'll bring that concept of "should I bring it or shouldn't I?"
I mean we already have enemies working with each other. It's not like it would be unheard of to see this.
I agree with this.