The VOIDRUNNER'S CODEX is coming! Explore new worlds, fight oppressive empires, fend off fearsome aliens, and wield deadly psionics with this comprehensive boxed set expansion for 5E and A5E!
I was thinking more of making it an at-will supernatural ability the Rock Lord can use as often as it likes, but make the rock-to-worm switch a move action and the worm-to-rock switch a standard action (actions modelled after ethereal jaunt).
It should also get some kind of Hide/Camouflage benefit when in rockform.