Undead only?

[Smash]

Originally Posted by Gatts

My fifth unit is Dark Commander (aka Black Knight)
slow unit but his morale bonus to my undead units is the bonus I like.

Yep - this was my final combination - I had red vamps, red bats, blue vamps, bone dragons, dark knights - but as I am lazy to pay attention, I used to transform accidentally red vamps into red bats - both units of red bats gone FRENZY (bad thing) - so in the labyrinth I changed the red vamps with green dragons.

I failed to understand, what are red bats? Isn't red bats and elder (red) vampires same? Did i missed something? I know that red bats are count as different units but how you make it?