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