I don't really get Urchin at #3. It's pretty nice (I have it at #11), but it's not that good imo.
Urchin itself is a weak attack and a cantrip, nothing too special. If you ever buy it, it's because you want a Mercenary, a card that looks ridiculous at first glance - trash 2 cards, +$2, +2 cards, AND a Militia to boot. However, best case scenario, if your two opening Urchins collide on T3/T4, you can only start using Mercenary after the second shuffle. If they don't collide, you need to wait ANOTHER shuffle AND probably need to invest in another relatively useless Urchin. By that time, you should have been busy trashing with an early-game trasher if available, or just building in general.
Then when you finally have the (admittedly) very strong Mercenary, you can start abusing it, right? True, but you will likely run out of Mercenary food quickly, especially if you decide to go for more than one. And if you can't trash two cards, all of the other abilities will stop working as well... so you either have to sacrifice good cards, buy a lot of Copper (and get lucky enough to make it line up with the Mercenary), or stop using the Mercenary altogether.
So all in all, Mercenary is very powerful, but there are a lot of factors that balance it out. In my opinion Urchin is nowhere near the leagues of Ambassador or Masquerade.
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Also, Steward and Amulet should be right next to each other. They're both very strong and fulfill very similar roles.