Paulmall originally came up with the category and initially named it Completionist%. Hypnoshark then renamed it to Max% (source). There are also Max% categories in other games Hypnoshark is involved with, such as Crash Nitro Kart, Crash Team Racing, and Spyro.
This thing from an old version of the game could be useful for Max%; maybe the code is still in the game somewhere (link)
When all 100 Crystals on a level are obtained, a singular Crystal shows up on the screen, and is shown on the pause menu as well.
