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