A BrainDie

A_BrainDie is a code pointer used in the death animation for the Big Brain.

immediately exits the level, analogous to pressing a level exit switch or crossing an exit line special type. It is used for the last frame of the boss brain death sequence for the final level.

Uses
The  code pointer appears in the following states in Doom's state table:

Example
The following is an example of how to set the  code pointer in a Dehacked file:

Pointer 21 (Frame 34) Codep Frame = 783

Or using BEX syntax:

[CODEPTR] Frame 1234 = BrainDie