In the "Talisman with Sir Martin" thread it was ruled by Donald X. that you could gain a Silver with Trader off the "first copy of Sir Martin that you were about to gain with Talisman". You "would gain" this imaginary copy before the actual Sir Martin you are buying. And then you could get another Silver or the regular Sir Martin which is still there the second time around. I.e. there doesn't have to be an actual physical copy of the card in the supply for Talisman to activate before the regular gain.
Now it's interesting to ask if this also works with BM because as specified, regular gains work with the regular supply.
The timing would be something like this:
- Buy a Treasure Map or whatever from the BM deck (note that you have not gained anything yet at this point)
- Talisman activates and wants to gain a copy of the card and the possible rulings present us with two choices:
- It wants to gain from the same source (the BM deck), it still can since the copy is there and you can pull off the same Trader trick as with Sir Martin
- It wants to gain from the supply and it fizzles since there is no Treasure Map in the supply
- Your regular would-gain of the Treasure Map off your buy now activates and you can do with it what you want, reveal Trader or not
I think the second choice is the right one.