MArcomage

As much as I don't want to admit it (I like my Brigand deck), this card is too good in it's present format. Playing this with 3 or 4 brigands in your hand is crippling for your opponent and will usually win the game for you. I suggest either lowering the base stock stolen to 2, or lowering the cost and cause it to discard the Brigands (this would provide cycling, which is helpful in any deck).

Discard won't make it weaker

Not by itself, no, but it would cause people playing a Brigand deck to want to wait until after they'd played the more useful Brigand cards in hand before playing Thievery, resulting in it hitting for less and giving the opponent time to discard it.

Also, Brigand decks succeed by flipping the counter preferably every other turn. This requires 5 Brigands in hand at all times. By playing Thievery (if it were to discard Brigands), you reduce the number of Brigands in hand (because statistically you aren't going to replace 5 Brigands with 5 Brigands every time), thus reducing the efficacy of such decks.

If the discard were implemented however, I suggest that the cost of the card be reduced to around 10.

You have to consider though, that Brigand decks deal damage very slowly and use up massive amounts of recruits (much higher than the amount they are gaining). Thievery and Prince of Thieves are the only 2 Brigand cards that actually do give you back a good amount of recruits (Prince of Thieves gives you a gain, Thievery is basically played almost free with a slight loss), and thus make Brigand a balanced deck. The Discard effect might be a good idea, but I don't think the stock "exchange" should be reduced. It will make it much more weaker than the desired effect. And don't forget, it costs 13 recruits, it deals no damage at all, it's not a keyword card and probably after you play it you will end up with less recruits than before you played it.

As I said though, the Discard effect is a good idea, but an even better would be to replace all Brigand cards in game with Hidden Treasure, or non-rare non-keyword cards, etc. i.e. an effect that will make someone use this card only when he thinks its necessary to block the opponent's strategy.

Replacing ALL Brigands by useless cards would be comparable to playing cleansing on yourself as Undead player: suicide.
The resources stolen should be doubled before that's worthwhile.

If this card would really need a balance change, raise cost by 2 or something, or cap N on 2-3.
The base steal is useful when splashing Brigands in other decks.

I agree about this card being too powerful. I'm really not sure if having it discard the brigands would make it more or less powerful, though.

Judge is common and can counter that card.
I mean for 0 you can "rollback" 50% of the effect (like other cards).

Yes maybe its a bit powerful in theory but in a game I do not find it that much powerful (maybe changing only the +4 for +3/+2)?

If this card is indeed overpowered, it only is in Brigand decks. Ive splashed it along with some Brigands in my Mage deck. You'd have a hard time convincing my it's overpowered there.

As a consequence of the above, the possible balance should be in the Brigand synergy, not in the fixed part.
Cap it, divide it by 2, things like that...

Old version had 11 stock stealing. This one has 13. In most cases it is better than Prince of thieves, and it doesn't have any restrictions. By the way, there are 3 Brigand summoners, 2 of which are able to summon it with very high probability.
Maybe cap it somehow or implement some more non-common Brigands?

First of all, when describing a card effect, you should point out that you are talking about maximum achievable effect also counting keyword effect. So in order to have this effect, you have to have 7 other brigands in hand and token counter set with accumulated tokens. I was also confused when I read you post in the Infiltrator thread, because the numbers where off.

Prince of Thieves is cheaper and doesn't require other Brigand cards for it's card effect. So it's much more universal.

Yes, my bad.
But it's MUCH stronger than before. Brigand keyword makes it summonable with Pirate bay, Corsairs and Thieves guild, plus you need only 5 Brigands to trigger this keyword every second turn.
Prince of thieves is cheaper, has more effect in non-Brigand decks (that's why it's in top 10 played rares all the time), but it also has restrictions (not new, enemy stock > your stock) to have full effect.

I could raise its cost back to 15R or lower base stock steal.

Second is better - to 1 or 2. It could be compared with Catapult, but we don't have any Siege summoners, so I'd say 1.