Seeing as I'm nowhere near finishing the games I already have with 100% achievements, obviously I should create a list of even more excessive requirements to reach "true completion".

Assume that any requirement listed is in addition to 100% achievements, if applicable.

A few minor spoilers ahead:

-BTD5: 100% map completion on normal/mastery.
-BTD6: 100% map completion on all maps and all difficulties, get 1st in a race/one of every race reward, all instas
-BMC: Place all buildings (max amount), control the entire map
-BTDB2: All towers maxed, all cosmetics obtained, reach HoM
-NK Archive: Complete every game contained 100%.
-JSAB: All S rank normal/hardcore, (unknown number) of beat points for rarest icon
-Super Hexagon: Reach 60 seconds in the Final Hexagon from every level
-VVVVVV: Complete all included custom levels
-Pivvot: Reach 100 sec on all levels/complete all levels deathless
-ShellShock Live: Max out everything (weapons, exp, items, etc)
-Celeste: All golden berries.
-Geometry Dash: Complete all in-game achievements, and complete all "officially provided" levels (map packs and worlds included).


Will add to this list as I come up with ideas.