No loss impossible unit combos.
 

I am currently in the early stages of a warrior no-loss challenge (not going for fast completion or anything like that, just no-loss), almost cleared Bolo and about 1/4th through the medals.

I was thinking about getting BK/Bone Dragons, but they alone give me kind of the impression that I'm cheesing the game.

What do you guys suggest for a legitimate 5 slot army? Are the other undead even worth mentioning here? Or would I really need a self-ressurecting remainder of the army, like Paladins, Droids or the like?

I was trying to think of a way to incorporate black dragons, but I've got no idea how they'd go through the boss fights.

Black, red, green, bone dragons. Archdemons. It is pretty soild, especially if you get time back.

Black dragons work fine in most boss fights, except the final two. It is really hard to keep a Black dragon alive vs Ktahu. You can just put them in the side board for that fight.

What about something that works with bone dragons + black knights? I was thinking maybe Black Dragons plus ancient vampires and liches, but I am unsure of the survivability of the latter two..

Ancient vampire are striker units, while they are awesome in attacking, they lack the defense. It's hard to keep them in full number during a boss/hero fight.

With warriror I only bring Vamps + Ancient Vamps to the fights against K'thau and Baal. because hugh leadership + flaming Eyes + staff with -15% leadership will allow you to have scores of them
and with the +6 attack after every kill and you get yourself a nice pair that regenerate so fast you can not kill them.