These are all separate pokemon
Gen 5, not legendary or mythical, was never featured in a who's that pokemon segment (reuniclus)
Sinnoh legendary, cannot be traded to scarlet/violet (regigigas)
Tied with Mega steelix for highest defense of a usable pokemon (Shuckle)
Has the same base attack stat as its final evolution but higher than it's first evolution, is base form/unevolved (trapinch)
Has crystals on its body, not available in scarlet and violet, not legendary or mythical (mega steelix)