Theres quite some luck element here, one good thing is if you see same upgrade in a row, the price wont change even if you used the first one, so make use of that to save money ; )
And when you see gold coupon use the elixir away and prepare for gaining a lump sum of monee!!
It's interesting the way the challenge is added, In epic mode Lord Tyrann absorbs melee attack, and i actually used a bunch of max lv magic army to defeat him.
The key is to spent the money efficeintly and farm on certain levels.
Btw, This game can be completed even without titans.
The best suggested path is to get Red upgrade till lv 3 ASAP, and get the Slayer Kara.
A combo of Red, Kara and werewolf is very useful in most stages, make sure they got full upgrade, and use pixies, then you can just sit back and win without even using mana, and win fast when the mana hits around 100.
 "Trigger Knight"){kind=icon}
 "Epic War 4"){kind=icon}
 "Semantic Wars"){kind=icon}
 "Black Navy War"){kind=icon}
 "Epic war"){kind=icon}
 "Kongai"){kind=icon}