tip: Once you upgraded gun cannon to level 3 there is no point to shoot all your bullets in magazine at once. You are dealing a lot more damage if you shoot very short series repeatedly.
TIP: To make the last battle realy easy build alot of titles around the dragon (I made a square 6x6). Adventurers (ones that survived, I had 3) will move around rarely attacking the dragon dealing some damage to it and then come back to walking around recovering lost HP (items increasing recovery per title are best). After some time your adventurers will easily kill the dragon. Please rate up, so everybody can see. Sorry for my English. I'm from Poland.
I have just completed level 58 and It's not that hard as it seems. Mine strategy: take energy homers, lighting and shortshield. Move close (not too much) to the edges and fire your weapons one after another, no aiming needed. Please rate up if I helped.