The supernatural Grim Reaper whose accidental use of Billy's pants sparks the crossover, later forming an alliance with Numbuh 1 to dismantle Mandy's KND takeover.
Mandy's takeover places her in direct opposition to Grim.
Mandy temporarily seizes control of the KND before being confronted by Grim, who helps dismantle her takeover.
Billy's accident directly involves Grim's supernatural artifact and triggers the crossover.
Billy accidentally gets stuck with Grim's scythe in his dad's lucky pants, creating the central problem that brings the characters together.
Explore the full interactive character relationship map of The Grim Adventures of the Kids Next Door