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