Are you talking about the baron's mount, that looks exactly like the undead warhouse only blue instead of green or purple? If thats the case you'd be much better off just farming runecloth to get exalted with undercity and buy the warhorse in purple/green instead - no one will even know the difference and it will be about 1000x quicker since the drop rate is like 0.001% (lowest drop rate of any item in game as confirmed by multiple GMs).