Hearthpwn

100% looses to pirat war

What do you mulligan for and how to deal with pirates? Just lost to 2 in a row. I caved, became pirate and beat this deck.

Board control is everything against Pirate Warrior. Mulligan for one-drops (voidwalker obvs, but Flame Imp is good as well to help you get early board presence) and buffs, make clever trades and don't discard too much early in the game. You'll take a lot of damage, but eventually, your opponent will be out of resources, and if you've kept the board, you can now begin to push face damage. But keep his board clear at all times! I very rarely loose to Pirate Warrior with this deck (I've just beat three in a row.)

Any reason you've excluded Tiny Knight of Evil? Seems useful here, even if you cut a Voidwalker or a Gang Boss

If you want to use Tiny Knight, don't cut a Voidwalker or an Imp Gang Boss, too much value is lost - Voidwalker is essential in matchups against Pirate Warrior, and Imp Gang Boss is great with the buffs, especially Crystalweaver (buffs the tiny imps as well). Cut a Darkshire Librarian if you must - I personally prefer the extra carddraw. 

I play something similar to this, but remove one Librarian for a Blast Crystal Potion to get rid of those annoying taunts or trouble like Rag if you go into later game