Here is the full list of all 19 Doki Doki Literature Club Plus! achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Achieve 100% data collection.
Spend 20 minutes listening to music on the desktop.
Review Paula's project plan.
Finish all of the Side Stories.
Draw boxes on the desktop.
Find Dan's special note.
Write a perfect poem for Natsuki.
Write a perfect poem for Yuri.
Write a perfect poem for Sayori.
Delete Monika twice while getting deleted zero times.
Write a poem in 20 seconds or less.
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Love, Monika
Ruin the game.
Choose not to quit DDLC.
Listen to a lot of what Monika has to say.
Write a perfect poem for Monika.
Start a New Game.
Spend enough time during the poem minigame for the music to loop.