If you're LUCKY, you can defeat the apprentice with a weak ranged party. If SOMEHOW the apprentice got stuck, keep hitting him while using PI as often as possible. He gives a hell lot of LPs.
Specialities:
Humans: Not much, only very strong paladins and their electrifying attacks.
Elves: Incredible combinations between their dryads and p.archers which doesn't give any chance for enemies to come close unless in great numbers or fatso with lots of health.
Orcs: With a hell lot of totems charging the enemy castle in one go, the enemy castle will be crushed even before their superior units (dragons, angels etc.) reach your totems.
If you want to fight auto for defense while avoiding the chance to lose a castle, save before ending your turn and exit if you lose a castle after ending your turn. Then just press continue, the outcome changes most of time either the enemy won't attack or you succeed defending.
Build a tazer next to a cannon. upgrade the cannon's rate until you get the freak out, of course after enabling the combo mode by fully upgrading the damage. freak out will cause the tazer to taze like crazt, useful for slowing down large number of enemies.
Just for a tip to get maximum invisibility for quite sometime : pick bacteria, sell all symptoms, buy all resistance and leave everything blank including transmission. Works really well to infect all countries but still madagascar will be a challange.
I don't really know how to activate the baron's skill, but i think that if his focus reaches 0, he will use a skill that restores his focus and damage him for 3k about 2 turns if i'm not mistaken.