I suck with Pythium ... please help!

[Cohen]

An Illusion coundn't kill.

Well against a F9 blessing you go for some horrors slowing Marignon guys and you kill via orb lightning.
However Caelum is more mobile than Marignon. So he can avoid your flagellants and paladins, that couldn't be everywhere and take all undefended province.

If you choose to advance in his land with an army he'll death rout it by surrounding it taking all provinces and sending in a little bigger expedition force.

[Chazar]

I do not say that Caelum is helpless against Marignon, all I am saying is that Marignon is not helpless against Caelian horrors - and that I do not use false horrors against foes like Marignon as Caelum myself, for I find them to be too weak...

Hmm, I've never ever met an Illusion that I realized as such, but according to most fantasy-magic-rpg-folklore that I am aware of, Illusions usually kill quite well...