What 5e monster would it be best to give a headband of intellect? And how would this likely change its behavior?

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I feel like this would make for a very fun encounter somehow provided the right option. So far, my vote goes for Hydra, since with intellect and planning, it would probably be able to retreat to water and and rest up, stockpiling heads for future battles. It'd also gain elements of planning, and be better at facilitating ambushes from the water.

(I'm presuming that monsters of any size can wear the Headband. I just want to see what people will come up with.)