last boss was easy. did it on the first try no lie. Go back to the older levels and grind people :D Leave it playing while you listen to music or play other games.
If you want to do 500+ damage just take one of those Mysterious " " of Death items then use it. It'll get 400+ with every hit.. but you'll die after, so it doesn't really matter as long as it registers with the system.
 "Boombot"){kind=icon}
 "Epic war"){kind=icon}
 "Achilles"){kind=icon}
 "The Last Canopy"){kind=icon}
 "Chronotron"){kind=icon}
 "Castle Crashing \"The Beard\""){kind=icon}
 "Sonny"){kind=icon}
 "Boxhead: The Zombie Wars"){kind=icon}
 "Feudalism"){kind=icon}