You need to find all health upgrades and cassettes and abilities. 6 abilities you pick up in maps, 2 of them are given to you after you get 7 and 14 cassettes by talking to the frog in Nexus. The developer notes are not needed though. Here is a guide to find all upgrades: https://gameplay.tips/guides/4264-gato-roboto.html
Be aware that there is no NG+ and once you ride the elevator down to the final boss there is no way to get back up. Yes, that's right, the game completely locks you out by auto-saving after killing the final boss. Again. Do not take the big elevator in the lab area down until you have 14 cassettes and 10 health upgrades.