A Metal

A_Metal is a code pointer used in the normal animation for the Cyberdemon and Spiderdemon.

is a wrapper around A_Chase that also plays the sound effect DSMETAL. It allows the normal monster chase AI to run while adding sound effects for the boss monsters' footsteps.

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 = 682

Or using BEX syntax:

[CODEPTR] Frame 1234 = Metal