All I've thought of would be: Sound SE against Water and Ground (reverberates easily), Psychic (puts them off), weak to Ghost (too scared to speak), Poison (throat infection?)
Light SE against Dark (hurrdurr), Ghost (ghosts avoid bright lights, etc), NFE against Fire (already generates light), Water (water refracts light), and Grass would be immune to it (photosynthesis)
Haven't thought about resistances too much, or gone in to too much detail with these. It does, however, balance Ghost/Dark types somewhat, give the Starter trio some more pros/cons (water was a little OP, Fire and Grass better defensively), and boosts Poison somewhat. Rebalancing is fun.
It'd make some pre-existing pokemon more unique too, but I'll cover that later.
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