ZDoom

I can't remember. The error came in when I added the DECORATE version of the Revenant. These definitions were taken from an older project of mine so the change was most likely not related to ZDoom.

Changed back.

The only thing I can think of is a possible infinite recursion, but I don't see one that can be caused by A_FaceTarget, as it doesn't set anything other than angle and stealth visibility.

I seem to recall that this was done for a good reason but I do not remember what it is precisely.

    {SPR_SKEL,32777,0,{A_FaceTarget},S_SKEL_MISS2,0,0},	// S_SKEL_MISS1
    {SPR_SKEL,32777,10,{A_FaceTarget},S_SKEL_MISS3,0,0},	// S_SKEL_MISS2

    SKEL J 1 Bright A_FaceTarget
    SKEL J 9 Bright A_FaceTarget

In Doom, the revenant's first two attack frames are defined as:
[code] {SPR_SKEL,32777,0,{A_FaceTarget},S_SKEL_MISS2,0,0}, // S_SKEL_MISS1
{SPR_SKEL,32777,10,{A_FaceTarget},S_SKEL_MISS3,0,0}, // S_SKEL_MISS2[/code]

However, ZDoom moves a tic to the first frame:
[code] SKEL J 1 Bright A_FaceTarget
SKEL J 9 Bright A_FaceTarget[/code]
While it's not really a game changer, it is still visually different (although hard to spot).