Shortcut by krushThis likely makes money more viable with the basic non-mirror-anti-engine strategy being: get an early Province while the other dudes are still building up, then trigger Shortcut knowing that they cannot hit $8.
So while this looks simple and straightforward on the surface there is more depth as it leads to a nice meta.
6/10
Crowded Village by NoMoreFunI most like that this is a $3 and not a $4 Village variant. In a 2P game this is fine, when there is an even split and the players are able to draw their entire deck they can trigger the game end whenever they like.
I dislike that this scales badly and is basically just Village in 3P.
5/10
Circus Maximus by LTacoI don't get this. You need a lot of turns with several shuffles which is only possible in a draw engine with discarding. Even then, it seems unlikely that the extra shuffles compensate for the non-shuffle turns.
1/10
Eye for an Eye by grepMan, this is cool on so many levels. Compensates against Cursers, keeps whoever got lucky and got a Curser early in check and last but not least there is the Ambassador-like (there is no to-and-fro thou) minigame. Like with Ambassador it could situationally make sense to buy a Curse just in order to spread it around.
8/10
Federation by Will(ow|iam)This leads to a horrible endgame slog as you always want to get Provinces, then Estates (more Coin-VP efficient) and then Duchies. In all games. No three piles anymore or whatever, just Provinces-Estates-Duchies in all games. Nah.
0/10
Lost Empire by JWThere is no price so I guess it is supposed to cost $8 like Enclave. Obviously a monster splitter is better in an engine than the Golds from Enclave. But precisely because they are monster splitters the marginal benefit of each extra monster splitter is small, so you have no incentive to empty the pile and there is an anti-synergy with the "counts as two piles" thingy.
4/10
Great Library & Lost Book by EthanExcept for not scaling well in multiplayer this minigame is really cool.
7/10
Traveller line by fika monsterLittle Picker is fine, weakish $2 as starting point.
Collector is easily my favourite here. Vanilla-wise it is a Worker's Village with the Flagship-like can-trigger-later aspect. The type thing is kinda weird though (you know that Travllers above the $2 are exchanged into and not gained, right?)
Marked has been described as overpowered by other posters but you might very well have to trash good stuff which is probably the idea here, to kick start Garbage Lord.
I assume that Machinator works not as written but with the extra play you described. Trash + TR/KC from discard is pretty wild and totally OK for the $5 in a Traveller line
You made a wise decision to give Garbage Lord decent vanillas. The Coin treshold has to be large enough to not make Garbage Lord too centralizing but $30 seems excessive. Unless there is TfB like Remodel (Golds) or Forge/Salvager (Provinces) I don't see how expensive stuff lands in the trash. If Marked makes you trash good stuff, you want to trash Silvers or whatever.
Then again you can set up a megaturn in which you use Marked and Machinator to get expensive stuff into the trash in this very last turn.
I gotta be honest: I am not the hugest fan of this idea and somehow not totally convinced but man, this is incredibly hard to judge and the idea is very creative.
9/10
Check by AugieSimple and good. I did not expect to see a decent extra turn concept but this is a fine middlegame Event for building up.
7/10
Door to the Land of the Dead by LibraryAdventurerSo this converts 2 buys and 8C+6D into 7VPs. One extra VP relative to Province+Lab with a similar cost. But whereas the latter empties two piles, this does not.
2/10
Reserve Army by Roving BearThis is too good. The vanillas are fine and e.g. better than Merchant Ship (which says little given how weak Merchant Ship is).
Play-wise we know from Search that it is not that horrible to play one-shot terminal Silvers.
Then this gives you great endgame control and does not work well in multiplayer.
3/10
Prestige by AquillaThis is brilliant. Majority for VPs is not novel but combined with a mandatory endgame trigger this converts a straightforward majority mechanic into something sublime.
The numbers might need some work though. With 24VPs as a benchmark from an even Province split, Prestige only creates a VP delta of 4. That it likely not enough.
10/10
Golden City by BryGuyVanilla-wise it is Fugitive+Village so a $4.5-$5.
The most obvious sin is that this an engine card that self-junks you with yellow.
Then there the pile thingy which is unlikely to even do something (the card won't see 30 plays).
0/10
Valley by AJL828This feels like it hits a sweet spot concerning how easy/difficult it is to trigger the alt game ending condition.
I also like the engine synergy. You want to play an engine more with more green in the Kingdom and the engine makes it more likely that you draw 5 different Green.
9/10
Disjointed City by SignErrorThis is such a great City variant but it is marred by the endgame slog. So with some slight rework this could become a fantastic card.
5/10
Runner-Up: The funky Traveller line by fika monster which wants to kill the expensive stuff, Aquila's Prestige concept with some possible implementations that makes you want to invent a zillion cards with this mechanic and AJL8282's Valley that is much more than vanilla 4VP for $6 green.
Winner: Prestige by Aquila