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