No missable achievements (plus 10 unknown)
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Completed the game.
Guessed the combination to Oscar's safe before finding the code.
Opened the secret bookshelf in the guest room from the outside.
Returned Christmas Duck to his rightful place.
Found Mitten's secret diary.
Turned on every faucet in the house at once.
Completed the game having found all 23 of Sam's journal entries.
Completed the game in less than 1 minute with no Modifiers enabled.
Activated all Commentary Nodes with the Developer Commentary Modifier enabled.
Completed the game having found all 24 journal entries, without Modifiers, in less than 10 minutes.