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