Amagon for Nintendo (NES)
In Amagon, you control the title character, a decorated Marine who is
sent to investigate the six zones of a dangerous, monster-infested
island. You start out weak, but after earning 5,000 points and finding
the Mega-key, you're able to transform into the powerful Megagon. This
alter ego can survive multiple hits depending on your point total, which
encourages you to kill more enemies and take more risks.