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.
Finish all of the Side Stories.
Spend 20 minutes listening to music on the desktop.
Draw boxes on the desktop.
Find Dan's special note.
Delete Monika twice while getting deleted zero times.
Write a perfect poem for Yuri.
Write a perfect poem for Natsuki.
Write a perfect poem for Sayori.
Love, Monika
Ruin the game.
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.
Write a poem in 20 seconds or less.
Review Paula's project plan.
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Choose not to quit DDLC.