I was playing dominion this afternoon and I gained 4 cards during my buy phase with a single buy1, this was pretty impressive, however this got me wondering: What is the theoretical limit to how many cards can be gained with a single buy?
Some ground rules to further clarify what I mean:
Only cards gained during the buy phase count.
As suggested by Joe W and GendoIkari only cards gained after you purchase something count. (for example using loans to discard tunnels doesn't count as gaining)
You may only use one buy even if you have more.
We only count cards that are kept until the end of the turn. If a card is gained but trashed it does not count.
We care about only what is theoretically possible, not what is reasonable, so you can dictate:
What other players choose to do
Shuffling outcomes or any other source of randomness
But the result must still be possible, meaning that there must be some path through proper play that arrives at the turn and all moves in the turn must be legal.
You may choose to play with any number of players.
To keep the scope a little small I would also like to ignore black market.
Just thinking about this on my own I came up with a way to gain 75 cards now 141 cards in a single buy which I posted as an answer to get the ball rolling. I had a lot of fun coming up with it but I'm sure someone who knows the newer sets can come up with something way better.
1: I bought border village, which allowed me to gain cache which gave be two additional coppers (which I ended up turning to silvers with my trader)