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Nu Base Stats
HP (=Steelix)
>75
Attack (-20 Steelix)
>65
Defense (-40 Steelix, =Onix)
>160
Sp. Attack (=Steelix)
>55
Sp. Defense (=Steelix)
>65
Speed (+60 Steelix, +20 Onix)
>90
This follows the model of Scyther's evolution into Scizor, which maintains the same BST by taking points from Speed and putting them into attack and Defense.
I would also give Onix some new moves, like the Coil+Glare combo given to every other snake. Violate makes it statistically bulkier than Steelix but with a much worse defensive typing. But the decent speed makes it rare among very defensive mons, and lets it perform a supportive role in 2v2 better.
So if you don't want to evolve Onix, it's mostly better in PvE and you can take it through the game. But like Scyther you still get lots of benefits from evolving it.
