Heroes 5.5 WarGame Edition - Tactical Edition.

Wyverns, Aspids, Paoka

But an asp is a snake. Literally. I don't know any other meaning for this word.
I agree with wyverns and paoka, good choice.

Another option: butchers (although the associations aren't quite right, it's more from Warcraft).

I like it.

Specifically, these units attack with lightning, but in general, the alt-tier has a distinctly icy theme (priests with cold, ice dragons).

Lightning is lightning.
Ice is ice.
Actually, there's a mod somewhere online that reworks the towns into a water/ice theme.