The character of Drahmin is an interesting concept. True, he would have been cooler as his original design (a living weapon for Quan Chi), but he's fine as is.
It's his gameplay that suffers hard in Deadly Alliance, and it's inexcusable. He's slow, awkward, and has limited combo potential. The MK dial-a-combos may suck, but in a game where they're the bread and butter of the engine, you don't introduce a character that can't do 'em - it's just asking for the player to fail.
Worse yet, he's an unlockable character, meaning only completionists will want to uncover him. At least Capcom could get away with ferreting Dan away as a secret character in most games because he's a joke, and can actually be deadly in skilled hands. Drahmin is just overall sad.
Drahmin was once a man, sent to the Netherrealm thousands of years ago and left to rot. He eventually became an oni, living for nothing more than to inflict suffering onto others. Along with Moloch, they saved Quan Chi from the wrath of Scorpion in return for escape from the realm. Quan Chi lied to them and escaped on his own. Shang Tsung found Drahmin and Moloch and used them as standbys in case Quan Chi turned on him.