Ghosts to Glory profile
Above the Grim Reaper's Limbo dwelling, King Achille's gargantuan drill is tearing apart the Underworld and gathering all the spirits of the dead. Without these spirits, Grim will have to hang up his sickle and retire. His only hope lies in the arrival of Maximo. The two strike a deal: Maximo collects the remaining spirits in the outer-world, and Grim lets him live.
Army of Zin profile
Grim is still the keeper of the Underworld, and now a close personal friend of Maximo. He not only grants Maximo free trips back to the land of the living in exchange for freeing souls from within the Zin, but he'll even help out in battle too. And since it's impossible to kill what's already dead, Grim is an invincible, sickle-slinging wrecking crew!
Partnership with Maximo
In Ghosts to Glory, Grim allows Maximo to return from the dead after players loses all their lives, at the cost of Death Koins. The price is one Death Koin the first time, but rises exponentially the more Grim is called upon (two Death Koins the second time, etc.).
In Army of Zin, his partnership with Maximo has grown so much that Maximo can now call on his ghastly friend to help in battle. As he collects spirits, the Grim Meter will gradually fill up. When it is full, it signifies the time that Grim is allowed to stay in the land of the living to help Maximo. Upon activation, Maximo will disappear for a short time and Grim will take his place in the fight. When time runs out, Grim is gone and player control shifts back to Maximo, so this ability should be used only in dire circumstances.
- Grim is probably a (or atleast based on) Skeleton Murderer, an enemy from Ghouls 'n Ghosts, although this has never been officially stated.