Best way to do the chain trophy is no to lvl up. Enemies will lvl up as you will, so get some points (like with the "collect all trophies" trophies) go to the game, lvl up your fire rate and spread, and stand still killing. You're not gonna lvl up, neither your enemies.
 "Unproportional"){kind=icon}
 "Deeper Sleep"){kind=icon}
 "Accelerator"){kind=icon}
 "Pixel Purge"){kind=icon}
 "Super Energy Apocalypse : RECYCLED!"){kind=icon}