completionist

[ kuh m-plee-shuh-nist ]
/ kəmˈpli ʃə nɪst /

noun

(in a video game) a player who attempts to complete every challenge and earn every achievement or trophy: I’m not really a completionist, so I skipped the side missions and focused on the main story quests.

Origin of completionist

First recorded in 1970–75; completion + -ist
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019