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