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- Merchant - Map created with 6 extra shops
- Negotiator - 20% item discount
- Opportunist - Gain gold for killing monsters
Tinkers are the class of choice for people who want to either make use of as many shops in the dungeon as possible, or to farm up gold in between "serious" runs. They get the most mileage after the player has done several runs through the bonus dungeons, since their wallet will be larger and the plentiful shops will begin stocking rarer items.
Because of this, the build for a tinker is largely defined by what the shops have in stock. If you get lucky, you could have an invincible death bringer who fears nothing. Shops are almost always useful in the long run, though, so you're unlikely to be screwed into a poor character.
Race and Deity Choices
Tinkers are the one class for which the Goblin race is a solid tactical choice (assuming you tend to gather up gold in between serious runs), since they can toss glyphs to get that last bit of cash for a neat item. If you're uninterested in that, you should probably stick with human or dwarf to play the odds and ensure a useful all-around character.
The really interesting choice for a tinker is Tikki-Tooki. Since it costs gold to join up, you need to ensure that you'll come out ahead if you gain the Gold boon, which isn't a very sure thing, so Tikki-Tooki is probably to be disregarded. The other gods' utility is as defined by the shops as the rest of the tinker's playstyle.