The Grim Adventures of Billy and Mandy (2001)

S1E10 Grim vs. Mom

Following her emotional collapse and departure in the premiere, Billy's mother, Gladys, makes her comeback. This time, she encounters Grim with an agenda to eliminate him for good. While Grim is in the kitchen grabbing a drink, Gladys seizes the moment to launch a surprise attack, breaking his skeleton into pieces. In the aftermath, Grim reassures the children that although Gladys may have triumphed in this encounter, the ultimate conflict is far from over.