Wyverns

There can't be more than 32 – it's been tested. Those same 32 Knights, with the right tactics, can take down the stack on their own. I didn't quite understand what you meant by RTA at first... Now I get it, and I can even agree with everything except for the fact that if they attack, they're not stupid enough to just cover the corpses... Or put something on them, or something else... And the Orcish flying units have serious initiative problems... So there's no guarantee that they'll eat up those large stacks.