Having first debuted in Modern Horizons 2, Grist certainly made enough of an impression to warrant a return. Unlike Wrenn, who returned in a few Standard sets, Grist returns in yet another Modern Horizons supplemental set.
Grist's Modern Horizons 3 appearance represents her life before and after her spark's ignition. She even has a Saga dedicated to her.
Sacrifice enough creatures and you can cheat in a big creature. Now if we can have some Magic Story or other lore on her, I'd be a happy Vorthos.