Do the people having difficulty realize upgrading armor restores hp? I completed all the achievements on my 3rd run with a lev 3 sword and lev 5 armor upgraded near the end for full HP. I bought a divine edge after using my freebie elixer.
Alternative to fire, 16 ice and 12 holy boasts 42% run speed, 100% mana regen, 38% crit, additional 54%(bonus 20% vs slow) damage, 67% faster firing on ice bolt. Simply spam ice bolt, blizzard, and heal as you need it. Had no trouble at all going beyond 600 score. Both work fine, I had more fun with ice due to the higher mana regen.