Not like Type:Null and Silvally though.
But I might remember wrong, so you could you make a few examples please?
Well, Slowbro is just a Slowpoke with a weird, mutant Shellder on its tail, and Slowking is the same, but with the Shellder on its head. I'd say they're comparable.
Same goes for Shelmet and Karrablast, in a sense, since they just lose and gain a shell, respectively.
Also, Silvally being its Evo and not an alternate form means that Type: Null can run an Eviolite set. Just thought I'd throw that out there