It adds an atrocious luck factor to the game.
Im not suggesting nerf undead, give them something else by all means buff them, but the plague is ultimately over powered.
War starts, I have 45% mana saved, make an attack get the plague. Burn through all 45% mana and still have it. Getting hit now by enemies that could not otherwise have broken me. This is a STRATEGY game revolving around teamwork, and plague drastically alters strategy.
Been meaning to write this suggestion for a while now. In every single war this age my mages have been "exhausted" all throughout it. All the fun stuff like casting quick feet and putting up magic shield and trying to town watch bounce people gathering intel isn't ever even possible. I would say plague LIMITS the game rather than enhancing the thought/strategy behind it.
Now I am faced with logging in every tick from work to cast NB and hope to win the lottery on a 1/5 chance. Or im spending the first 24 hours of a war with the plague, completely altering my strategy and plans for the war.
Same thing every war... But there's no way to counter it or plan for it.