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