I didn't know it had a clone. It's also important to attack yourself, as if it attacks, it will split the titans.
With the help of speed artifacts, you can give harpies 12 speed, the same as the titans. I don't think I'll have enough mana even with mages.
Added 5 minutes later
If the harpies and phoenixes tactic doesn't work, then the second way is to kill them with sorceresses, but I don't think they will deal more damage than the harpies.