This is by Manik668 and follow everything what he said in the comment it helped me kill the first Epic 100% :)
You were asking for help on "the epic" and if you mean the first epics boss, then do exactly what the strategy guide tells you to, but abandon the water trenches and use mana pool until your mana is in the 6000s and while building around seven other towers all in one area.
After you do that, get at least one grade 6 gem, and then get grade 4s and 5s.
When it gets to the 26th wave, stop buying everthing if your mana is 6000 something and speed it up and wait.
when the boss gets there, just make sure that you have more than 4500 mana and you should be fine. Hope this helps.