Solomon Grundy is first seen in the bowels of Arkham Asylum, being contacted by Harley Quinn, who promises to turn the dampeners that are keeping him contained off, in return for destroying the Asylum. As Harley releases the inmates, Grundy bursts from the floor, chanting his namesake nursery rhyme as he grabs hold of Robin and drags him back under the Asylum, ignoring the combined attacks of Superman, Wonder Woman and Green Arrow as he does.
Grundy is still holding Robin by his head while Wonder Woman stabs his upper arm, though this only prompts the beast to backhand her with enough force to send her through several walls. Grundy begins to return his attention to Robin when he sees his wrist begin to smoke before falling off. Staring dumbly at his smoldering stump, Grundy turns around in time to see a grinning Superman just as the Man of Steel smashes through Grundy's chest in a spray of gore. This seemingly fells the monster, but only for a few moments.
After Nightwing frees Robin from the zombie's severed hand, Batman arrives and Grundy revives. Robin and Nightwing are ordered to return to the Asylum above while Batman charges towards Grundy, leaping over him and slamming two explosive devices onto the sides of his head. As the Dark Knight lands, they detonate, decapitating the monster and finally subduing him.
Though not seen, Grundy is moved to the location Superman had been planning.