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