>>39280959I'd basically match his stat total with Steelix's, basically mimicking Scyther's evolution into Scizor with the Metal Coat by dumping speed into attack and defense.
Old -> New
35 -> 75
45 -> 65
160 -> 160
30 -> 55
45 -> 65
70 -> 90
385 -> 510
Onix gains better attack, defense, and typing upon evolution, but Onix gets its own niche with it's own typing and decent speed.
Onix still could use a few tools, so I'd give him snake moves like Glare and Coil. Glare will improve support sets with Onix's existing support like Taunt and Wide Guard. Coil can be used in meme boosting sets alongside Weak Armor for expert humiliation of your opponent. Last but not least give Head Smash so it has a reason to run Rock Head.
There, I fixed Onix /vp/.