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