They are hell with Persephone... You can rush them with Ents or Trolls though, but there are 4 of the Magnafryers with her.
With James it's completely opposite. Just summon 10 Troggs and you're done. They're immune to the Magnafryer's beams.
Btw, I HAVE beaten this game with every single combination that is possible.

I didn't have too much trouble with the magnafryers, myself. The Ents' lifeshield protects them fairly well. The real trick is attacking the magnafryers in the right order (to wreak the most destruction will taking the fewest shots), and timing the activation of the lifeshield.
Charnel, now. THERE'S a devil who has issues with Magnafryers; no protection, and a wide margin for error and death. Oh well. Animate Dead solves everything, I guess...
James is the god of tanks. If you can get past the fact that nearly all of his units are incredibly slow (what do you expect from walking rocks?), you'll find that it's extremely hard to beat a massed group of his forces in a fair fight. Consider how difficult it is just to kill ONE Rhinok.

Yeah right, noob. There's hundreds -_-

And? It took me like two weeks...

Troggs are immune to the magnifryers attacks.