Game too easy actually...
Heres something to help you out. remember that you win by destroying the enemy castle, not the enemy.
Also, The shield (invinsibility) spell WILL be you bestfriend. make sure it it maxed out.
now to defeat the final battle (giant monkey) on epic, you need two spells, the shield and the hourglass (stop time).
what you need to do is set up some fast units like the weretiger and the flying ghost armor thingy and select fast moving heroes like tha main hero and the lady with the big sword.
Once the battle starts, quickly press the assault button so that your heroes will rush to the enemy castle. now this is very important because they will be able to get to the castle before the giant ape. The giant Ape has one weekness, it CANNOT hit whatever is under between its legs so it wont be able to attack the heroes under it for a while.
Keep using the shield spell once in a while and the time stop spell to send more units under the Ape.
Do NOT, i repeat, DO NOT use titans in this battle because they are veeery slow. You need speed in this battle, not power.
I hope this helps.