The Tark, a mutant horse, was made for the Monster Ball competition by GSC Gameworld in 2004. The prize was that the winner's monster idea would be implemented into the game, however the Snork monster won the competition, and the Tark was never implemented. Now in CoC as a new mutant, it is spread all over the zone and is commonly found near boar and flesh.
Greshnik13rs for the model and textures
Copy the "gamedata" folder into CoC dir, overwrite files if asked.
If/when you want to revert back to the vanilla files, eliminating the tark from the game, apply into CoC dir the "gamedata" located inside the "gamedata_backup" folder.