Madara Problem 

Sometimes called "Yhwach Problem" (after the second most famous case) Madara Problem is one of the most difficult writing conundrums: this one in particularly refers to a scenario in which a writer creates a character so monstrously overpowered and indestructible that nothing in the writer's universe is capable of killing the said character, and the writer is forced to either nerf the character to the point of destructibility (often defeating the character's original purpose) or killing them by an asspull.

Named after Madara Uchiha, a character from manga Naruto by Masashi Kishimoto. Reportedly, Kishimoto at one point admitted that even he himself didn't have any way of killing Madara, and had to resort to an asspull.
Alternatively named after Yhwach, a character from manga Bleach by Tite Kubo. Starting of as a high tier character, Yhwach was made nigh-omnipotent and immortal near the end of the manga, the combination of this and a tight schedule forcing Kubo to resort to a combination of nerf and an asspull to finally finish this monster off.

Ben: "Say, Jerry: this Dante character of yours is great, but he feels too OP. How does one kill him?"
Jerry: "I... I don't really know. I don't think anyone can. I don't think even I can."
Ben: "But you wrote him!"
Jerry: "..."
Ben: "Sounds to me like you have a Madara Problem on your hands."

Madara Problem by Helel ben Shahaar August 7, 2019