Here is the full list of all 20 Poker Night at the Inventory achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Win a hand with Four of a Kind.
Win a hand when you have three of a kind comprised of three kings (of any suit).
Win consecutive all-ins.
Win 12 or more hands.
Win a hand with a 6 card and a 9 card of any suit.
Win a game on hard.
Win a showdown with just a high card.
Win a hand with a Straight.
Win a hand with a Flush.
Knock out Max after he's bought in with his special item.
Knock out The Heavy after he's bought in with his special item.
Knock out Tycho after he's bought in with his special item.
Win a full game.
Win a pot with two or more opponents when you are all in.
Win a showdown where you and the opponent have same hand (pair or better) and you have a better kicker.
Check a pat hand.
Win three straight pots.
Knock out Strong Bad after he's bought in with his special item.
Win a hand with a Full House.
Win a hand with a Straight Flush.