droids vs necromancers? Sure, it a good idea to take -50% magic units to fight stacks that do magic damage, AoE magic damage mind you :D

it all depends what level are you, what spells do you have etc. Sure, 100 necromancers in 2 stacks are easy to beat with 150x2 repair droids, but is it easy to do it with 50x2? How about 20x2? Same goes for every other unit.

there is nothing easier that beating that dragon's lair on Montero, when you are level 40 with set of darkness, grinning stack of 200 Black Knights (+3 moral boost, always retalite) with axe of lightning and dragon slayer level 2 cast on them. They will slay those 150 dragons in 3 turns XD

as far as cyclopses go, casting helpness on them makes them tough as butter :D Casting Hell Breath on your paladins or whatever is going to have a go on them makes cyclopses melt, 10 or 50...doesn't mater, they are going to get 200+ % more damge then usual...

for me, brontors are thougest, especially if you can't magick lock them and they burrow. Pain in the ass reallly :/

repair droids, definitely

annoying like :M

Stacks of Alchemist have been a pain lately for me esp. in CW since they do an AOE poison damage that can hit up to 4-5 units and they can keep recharging their ability.