The urge to collect all the items, achievements or secrets in a game.
"There's a library in game that grants rewards for completing collections of monsters. Each monster is categorized into a "book" of up to eight monsters, and collecting all monsters in the book grants a reward. This is in addition to a global monster collection counter that appears when at your base."
"Used to have a collection system which rewards you for owning a certain amount of cars from a particular collection."
"The game has a page where all cosmetics are displayed for each character, showing blank spaces and a counter of missing parts of the "complete collection"."
"Seasons of card collections, large reward if you get all of them- but you get more and better cards by gambling more money."