to be simple, buy both the hero's, then just go crazy and max out the magic guys upgrade tree.
(its also very highly advised to buy sdome of popo's tree to get the bezek spell)
the magic guys tree has most of the over powered units, such as
pixy: better then the healing spell anyday!
sucubis: decimates units at range and sends them flying.
guild building: up to a 100% boost in money gain, need i say more?
alter building: up to a 100% boost in mana.
shield spell: up to 20 seconds, all your units become imune to ALL damage. not useing this = not winning.
and probably the best titan, sky dragon being only 1 of 2 titans that can damage shadow units (goblin maddnes, errghhhh...)
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now for some hints towards people who have unlocked the last tech tree.
this tree has 2 hero's, both of them are not overly strong, but there fast and still rather strong.
the one with the bow: allmost as fast as your first hero, but shes the only hero with a (reliable) ranged attack. a good allrounder that makes cood cover fire for your other hero's.
the slayer: now where talking! she is faster and stronger then your first hero, and her attacks are faster and throw units in the air. an exelent allrounder that you would be crazy not to use.
time stop: sort of like shield, but better, and cost more mana.
it makes all your oponents troops, 1. stop moveing, 2. stop attacking.
although its mostly not as good as shield, on goblin maddnes it can be epic.
huge-*** meteor spell (lol): if you need something killed, and now. nuthing beat it.
one hits shadow goblins (yes, you did read that right) and just plain destroys.
teh titans,
in order of roughly when you unlock them.
lord of fire: high attack, low defence. gets healed by bombs (not the big bomb though). his attack makes him move fast and thus is efective at getting past troops and in to, and destroying, the castle. very usefull at killing ba'al.
sky dragon: very usefull note, "non elemental attack", the only type of damage that shadow units can be hurt by.
imho the best titan, its attack is strong hits a large space.
that big bird like thing: slow but high hp, probably the least usefull titan.
angel: just totaly and utterly destroys small units, only titan with range, besides sky dragon. but she is kinda useless vs strong untis as her range jsut means she keeps attack one or 2 small units and does not move.
eh, thats enough for now.