Epic
Surely You know about all achievments by now as they have been mentioned about 100 times already. Here was my strategy for each boss...
The first thing was I always used humans. Also make sure that you have angel knights as well.
1.) Don't worry too much about upgrading anything but your barracks right away. The enemy will send in hobbits very quickly so bomberman is an easy counter for them. You need paladins up very quickly as a couple of them will take down a majority of the enemies troops. But don't attack the castle right away as that'll trigger the MASSIVE amounts of super units and regular units. Make sure you upgrade to arrow tower lvl 5.. that's a must for taking down super-units.... Then hold the enemy back until everyhting is upgraded and you have 9999mana.
Frog) This one is most challenging. What you'll need are to first send out the arch-angel out to take the brunt of his attack and to hold him back until you can send in reinforcements of arch-angel. Don't even bother with normal units with bosses.. would be pointless, or at least I didn't have to. The key to winning this one is to pummel him with arrows and keep the arch-angel up his ass to keep him from progressing onto your base.
Dragon) About the same strategy here except he's much easier with my before mentioned strategy of arch-angel then angel knights. He's much slower with rate of fire so over-time you'll take less damage then the frog thus easier to hold him off. Keep pumelling with your super-arrows. Also the arch-angel is great for taking out multiple super units at once while your angel-knights (super-dragon fist ) beam attack will keep the normals at bay.
Lord of hell.) A fucking joke. ONLY use 1 arch-angel at the beginning, the lord of hell will only attack ground untis and your titan unit is coded as a ground unit. So ONLY use arch-angel to destroy the castle/ keep back initial wave of super-units. Angel-knights and dragons are the key to winning.
NOTE. Lord of hell will smash the ground on ground units. This will also do damage to your castle. Flying units are free from attacks of the lord of hell making this battle rather long but also VERY EASY.