Just got done beating the entire game. Great little game, can't wait for the sequel to come out, it's called "Gemcraft - Chasing Shadows". I won't spoil the ending for those who haven't finished Gemcraft - The Forgotten yet, but it's pretty neat.
The best way to get past the epic battles is to 1:get your mana pool up really high into the thousands 2lace wells all allong the path to slow him down a little bit then 3: place towers all along the path and move your gems along the predetermined path to kill him more efficantly.
All frames lit at lvl 78 It was impossible for me to get a lit frame at low level until I tried the bomb technique.
Last boss: Killed with ~10 lvl 6 pure gems, 6 water traps, and a ton of mana pool. Once you have 6 gems in place, and most of the water traps, keep boosting manapool till 40k ish, then start adding the rest of the gems. DO NOT spend any mana for the last 8 lvls. Setup an armor break (purple) where it will hit the boss on both passes. If you didn't roll at least 1 purple gem, you're screwed. Start over. Not sure how necessary the shock (Cyan) ones are, but they definitely helped.
I don't care what people say, orange gems rock for epics. I had 3 when I beat the last boss, and they drained enough extra mana for him to go around 2x more than when I started. Manapool boosts your score multiplier too, so if you're having trouble getting the lit frame on a level, try boosting mana to something ridiculous like 100k. Try to kill as close to the spawn point as possible, you get more points per kill.