>>45271134Bring Onix up to Steelix's base stat total, but take away attack and defense points and put them into speed, like so:
HP: 75
Attack: 65
Defense: 160
Sp. Atk: 55
Sp. Def: 65
Speed: 90
This purposefully mimics the Scyther/Scizor, which is the other Gen 2 Steel Coat evolution. It sets Onix apart from Steelix by giving it a more unique role as a much faster physically bulky mon.
Next, give it access to a few new moves:
Glare
Coil
Accelerock
Glare and Coil give Onix its long deserved "snake" status and are also pretty useful for both support and more offensive sets. Glare lets Onix provide great support while Coil synergizes with Weak Armor and Onix's inaccurate Rock-type STAB. Accelerock is just an excellent tool in general, and fits with Onix's more speedy theme.