Done! 50 deaths, 33 hours. Biome 4 and 5 were kicking my arse, then on a single run, got all three keys, and the next key and beat the final boss. Bit of a fluke I think considering it was my first time in biome 6. Weapon that changed it was the Electropylon Driver. My last run must have lasted 3 - 4 hours from the start of biome 4. Very good game and one I thought I'd never get close to finishing. Now time for the secret ending?