What would the maximum number of cards you could gain with a single purchase of Populate be? Obviously under normal circumstances, that would be 10. If there's a Looter and Young Witch, you'd add the Ruins pile and a Bane, making it 12. Plus ten Horses per Livery you have in play (Ruins and the Bane are both too cheap to gain Horses)
But some cards also have additional on-gain triggers. For example: when you gain Border Village, you also gain another cheaper card, so you could potentially gain two copies of an Action card - one from BV's on-gain and the other from Populate itself. If what it gains is greater than $3, then you'd
also get an 11th Horse
The maximum I can come up with is 61, requiring 2 (or more) Liveries in play and the following kingdom: Border Village, Hunting Grounds, Skulk, Young Witch, Death Cart, Catapult/Rocks (Rocks on top), Knights (Sir Vander on top), Catacombs, Graverobber, Livery, with Watchtower as Bane and the Innovation project having been purchased previously
- 12 cards from Populate itself
- All but the bane and the Ruins are $4 or more, so we gain 20 Horses (32 total)
- Skulk comes with a Gold, which in turn comes with 2 Horses; a total of 3 more cards (35 so far, incl. 22 Horses)
- Border Village gains you a cheaper card, which we choose to be Catacombs, which we then trash with a Watchtower in hand to gain a Skulk, which comes with a Gold, and all in turn come with 2 Horses each, for a total of 9 extra cards (44 cards; 28 Horses total)
- Death Cart gains you two more Ruins. Since Ruins are $0, they don't bring any additional Horses (46 cards)
- Rocks gains a Silver when gained (47 cards)
- But wait, it also gains a Silver when trashed, so let's suppose we have a Watchtower in hand and we trash the Rocks we just gained; that gives us a second Silver (48 cards)
- Port gives us a second Port, which in turn comes with the last 2 Horses (51 cards, all 30 Horses)
- The top knight is Sir Vander. We use the Watchtower to immediately trash Sir Vander, gaining us a Gold (52 cards)
- We trash our Catacombs with the Watchtower. We gain Skulk. Which comes with a Gold (54 cards)
- We trash our Hunting Grounds for 3 Estates (57 cards)
- We use Innovation on a Graverobber. Graverobber gains a Border Village out of the trash. Border Village comes with Catacomb, which we then trash for a Skulk and a Gold, 4 gained cards (61 total, including all 30 Horses)
So, 61 total cards, including all 30 Horses, 5 Golds, 2 Silvers, and 3 Estates.
Potentially all three Ruins are differently-named, so we have a total of 18 differently-named cards gained. If we
also buy Commerce, we'd get 18 Golds, for a total gain of
79 cards with just two buys - including
23 Golds! We've probably emptied out the Gold pile at this point
Just for the fun of it, let's suppose we have the Tomb landmark also in play, and we trashed
all of the cards, not just the ones specifically mentioned as being trashed. That gives you 79 VP in one turn! Or if we stuck with the 2 landscapes per game recommendation, we can leave out Commerce, and thus "only" 61 cards being gained and trashed for VP at a cost of just $10!
EDIT: Wait, just realized Port's extra Port is an on-buy effect, not on-gain, so that's 60 total, not 61, and 78 total with Commerce
