A BrainAwake

A_BrainAwake is a code pointer used in the normal animation for the Demon Spawner.

is activated when the demon spawner observes the player for the first time. It initializes the internal table of boss targets that are used by A_BrainSpit when firing spawn cubes. Secondly, it plays the DSBOSSIT sound effect, the infamous backmasked message of "To win the game you must kill me, John Romero".

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 = 785

Or using BEX syntax:

[CODEPTR] Frame 1234 = BrainAwake