If you breed two steelix, is there a way to make sure the baby is a steelix? Like giving them a hold item, like you do with snorlax and chansey.
No it will always be an Onix the only Pokemon that work that way are: Azurill, Wynaut, Budew, Chingling, Bonsly, Mime Jr., Happiny, Mantike, and Munchlax.