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Holy shit, why aren't people getting more hyped about the DexNav?
This is an incredible feature.
You can lock onto individual Pokémon and, after levelling up the DexNav, you can find Pokémon with new, special moves that can only be obtained using DexNav, you can find their level, find their Hidden Ability and - best of all - you can make sure you're getting one with good IVs.
It's also got the ability to register Pokémon you see in the environment, outside of battles, in your Pokédex. Say you go to a house with a Slakoth inside, and you've not yet seen one. Boom. Registered.