How effective is earthquake for dealing with 20+hp mages? Also, does it affect friendlies as well?
I'm playing through some SP games, as I am very new, and I have a few nations throwing a lot of astral mages at me. I can't seem to script anything to deal with them before they mind burn me down.
Earthquake does affect friendlies as well including the caster. How effective it will be against those mages depend on how well they are geared and how many times you can cast earthquake.
Something else cool to keep in mind about Earthquake is that if you have a blessed caster casting it with a death bless, the spell benefits from the increased chance to cause afflictions.
Heavier armour and a shield is actually sort of a bad idea, since earthquake checks to hit versus defence, which will be garbage with that. Your mages will also all be extremely fatigued after the quake, and will probably get ganked.
Sticking on def items is probably a better bet. Parrying jitte, ice sword, cat charm etc.