If anyone has any additional information on this monster, that would be appreciated.
I created this page based on the information found in the Sokoban article.
I tried to find the mentioned public servers that had the acid hound, but was not successful. I tried to find the patches that implemented it and was found nearly nothing.
I did find http://slashem.airmack.de/hasteself/patch.diff and later the RGRN page that spawned this patch.
They don't discuss the acid hound at all, but from the patch diff, it looks like it implemented (or was patched against a version that implemented) the acid hound.
As best as I can tell, the public server with this version mentioned in the RGRN thread is dead, but then again my PuTTY client has been acting up today...
This is based off the Slash Em Extended "Pokedex"