Vertical Drop Heroes HD

Some good tips in the comments of FullMoonBeaver's solution, but I wanted to provide my own solutions. I tried lightning, firetrap, etc, but it was just not reliable. The most reliable and there's almost zero chance to lose with this combination, is to do this.

First thing is that you want a hero that has lightning and dwarf turret. The other traits can be anything but probably wealthy would make the game too tough. You can teleport to level 10 or start from any level, don't worry about saving keys or anything. If you want to skip a boss, try and get 5 keys. (I'd suggest skipping boss of level 10 if possible)

Now, immediately, place two dwarf traps under the left side hero, and then jump down left so you are hidden. Whenever the final boss comes near, use lightning. Repeat this, you will keep putting down more turrets and by the time 4th phase comes around, you don't even need lightning. Boss is completely, utterly, defeated using this method.