Say I target a living creature who is currently grappling someone with Boneshaker and they fail their save. I now get to move that creature 5 feet in a direction of my choice. Since the creature is being forcefully moved, does that mean it ends it's grapple or does it move the grappled creature as well?
The spell doesn't explicitly say that it moves itself, but that I move the creature with the spell, so the grapple condition preventing the creature from moving might not apply.
I would say no. You move the creature (it doesn't really explain how). I would say the grappled creature moves along with it. Maybe I would give a combat maneuver check to see if they keep hold.