Completionism
Also said as Completionist, 100%, Collect-a-thon, Coupon collector
The urge to finish everything a game offers: every item on the checklist, every marker on the map, the number to 100%.
A visible checklist turns optional content into unfinished business, and some people love that. Others feel it as a chore they cannot stop doing, so keep it opt-in. If items are random, the last few cost far more than the first, which is where collection turns into a money trap.
Say it
“Show the collection percentage only after the credits. During the story it pushes people off the path. And never give random drops to a complete-the-set reward: use a shop for the last few.”
Where you’ve seen it
Hollow Knight lets you push completion to 112%, which is a joke and a dare. Xbox achievements gave completion a public score starting in 2005.
Not to be confused with mastery
A completionist wants nothing left unticked. A master wants to do one thing perfectly. Someone can have every achievement and still be bad at the game.