Sidekicks Results
I too, wish we had a viable card called Adventurer (It's part of my username after all). But we don't. The original Adventurer would be fine costing $2. So it would take quite a lot to make it worth paying $6 for it. I will first address the two cards that were meant to go on top of Adventurer.
Trailblazer (by arowdok)
$4 cost - Action
Reveal your hand and discard pile. Trash a revealed Copper from both.
If no Coppers were trashed, gain a Trailblazer. If you can't gain a Trailblazer, gain an Adventurer and a Gold.
If you have no Coppers to trash, then you're not going to want another Trailblazer (you probably don't need a second one anyway). Probably the "gain a Trailblazer" part should be "trash a Trailblazer from the supply". So Trailblazer is a decent Copper trasher (which could probably cost $3 imo), but Copper trashing isn't nearly enough to make Adventurer worthwhile. (although getting the Adventurer for free helps.)
Vanishing Coin (by anordinaryman)
$3 - Treasure
Trash a card you have in play.
-
When you trash this, +1 Card, +1 Buy, and gain a Vanishing Coin.
I like this better than Trailblazer. Vanishing Coin is a nice Treasure/ruins trasher that trashes itself when you're done with it. It's a fine card, but it takes more than this to make Adventurer worthwhile.
Now, all the others:
Destitute Village (by JW)
$1 cost - Action
+3 Actions
+1 Buy.
+1 Card for each Raider you have in play.
(on top of Raider)
I like it. Villages and +buy are (almost) always in demand. We always want more than one village -unless there are other villages available of course, but then you might get it for the +buy. Raider is not so awful that it's beyond help, and it's not a card that's important to get early, so it's not hurt too much by having another card on top. Is there any reason Destitute Village costs $1 instead of $2? Thematically, it's a little weird for the village to like having Raiders around. But whatever. Theme isn't that important to this game in general. I also think it's a little weird for a village to go on top of a night card, which doesn't need actions.
FINALIST
Cupbearer (by Timinou)
$3 cost - Action
+1 Card
+1 Action.
Reveal the top card of your deck. If it's an Action, put it in your hand. Otherwise, discard it.
(on top of Prince)
This is nice and simple and it ensures there's always a viable target to play Prince on. It kind of looks like a fixed version of Sage. The fact that it's weaker than Herald gives it an excuse to cost $3, but it looks like it'll be pretty strong for $3 once you've done some building and trashing.
disclaimer: It's hard for me to judge a card that's supposed to go with Prince because I've only played with Prince a couple times so I have almost no first hand idea of how strong/weak it is. (I prefer playing IRL to online. I have almost every set, but not Prince.)
Old Boot (by Chappy7)
$2 cost - Action - Duration
+2 Cards.
At the start of your next turn, choose one: trash an Old Boot from the supply, or move the Boot token to an Action supply pile (card from that pile cost $1 less).
(on top of Cobbler)
I like the card, and as I mentioned, I like the way it's designed to go empty and works nicely with Cobbler, but (as faust said) Cobbler is a card you want in the early game so having a card on top of it hurts despite the synergy. I don't think they will go empty fast enough to help Cobbler more than it hurts.
FINALIST
Stablehand (by spineflu)
$2 - Action
+2 Actions
Gain a Horse.
The next time you gain a Horse this turn, gain an additional Horse.
(on top of Livery)
Livery is a good choice of card to nerf by putting something on top of it. And this is a good fitting card to put on top of it. I can't think of much else to say here.
FINALIST
Lockbox (by 4est)
$2 - Treasure
+$1, +1 Buy.
If you have the Key, +$3 and trash this.
(on top of Treasurer)
Another nice simple cheap card to go on top of a strong $5 card. +buy and being on top of a strong card should make it go empty without much trouble. The problem with this is the interaction of Treasurer taking it out of the trash and playing it for another $4. So instead of +$3, Treasurer basically gives +$7 (not including +$1 from the Key), which'll make it all the more frustrating for a player who can't manage to play 2 Treasurers in a turn (1 to take the Key and 1 to get a Lockbox from the trash). And there's no limit to how many times you can do it once there's a single Lockbox in the trash.
Scrying Bones (by Xen3k)
$2 cost - Action
+2 Cards
+1 Action
+1 Coffers.
Put two cards from your hand on top of your deck.
(on top of Mystic)
This is nice for Mystic. Mystic isn't specifically a card you need early, more often you decide if you want it at all. I think in the way that this helps Mystic be stronger, it also makes it less interesting. I think it's more fun to guess correctly with Mystic when you didn't use another card to peek. Then if you guess wrong, you can always play another Mystic. I guess I just don't agree that Mystic wants a card (in the same pile) to synergise with it. This is a pretty subjective contest...
Scrapyard (by Boomyday)
$4 cost - Action
+2 Cards
+1 Action.
Gain an Estate and a Silver.
-
When you trash this, +2 Cards, +1 Action, and gain a Duchy or a Gold to your hand.
(on top of Forge)
No one wants to dig through this much junk to get to Forge. Especially if it's the only trasher on the board, when Forge shows up, if you want it at all, you probably want it as soon as you can get it. You certainly don't want a self-junker if Forge is the only trashing on the board. Scrapyard might actually work better if Forge was on top and Scrapyard underneath it. That way, you can get Scrapyard once you've trashed down already, but it probably wouldn't be worth it even then.
Skeptic (by NoMoreFun)
$2 - Action
+$1.
Trash a card from your hand. If it costs less than this, +1 Card, +1 Action.
(on top of Mountebank)
A Junk Dealer variant for $2? Nice. Very strong for $2, but you could make the Chapel argument, that a card this essential should be easily available to all players. It should make Mountebank games less of a slog. Winning the Skeptic split may be just as important as winning the Curse split. In short, I like it, but I think it may be a bit too strong.
semiFINALIST
Projection (by Aquila)
$2 - Treasure
At clean-up, you may trash a Treasure you would discard from play this turn, to gain a Treasure costing up to $3 more than it.
(on top of Venture)
Venture is the official attempt to fix Adventurer, and Venture is actually fun and worth buying sometimes. Also, it's not a card you want early in the game anyway, since it's much better after you trash your Coppers. So putting this on top of it may help more than it hurts. It turns Coppers into Silver, then it can turn itself into a Venture once they're uncovered. Well done. Hopefully this isn't the only Copper trashing on the board though.
semiFINALIST
Land Survey (by xyz)
$4 - Action
+1 Card
+1 Action
Discard any number of Victory cards revealing them. $1 per card discarded.
(on top of Rebuild)
This is fine. I mean, the problem with Rebuild isn't that it's too strong, it's that it's an unfun, one-card strategy. This could maybe make it slightly more fun? The more I think about it, the more I think it could actually make it a little more fun. Rebuild itself would be weaker, not only because there's a card on top of it, but if multiple players are going for it, then you won't be able to get as many Rebuilds as you want before the pile runs out. It's been a long time since I've played with Rebuild at all (I use a modified version which is really a different tfb card with the same name), so it's hard to me to judge this, but it looks like potentially a good attempt at making Rebuild more fun. Just maybe, it could work better as part of a multi-card strategy instead of focusing only on Rebuild.
semiFINALIST
Goshawk (by mandioca15)
$3 - Action - Reaction
+2 Cards
———
When you play a card that has two or more types, you may play this from your hand.
(on top of Falconer)
A card with this text really should be a blue dog, imo. Anyway, this seems like a fine card, but I don't really see that it goes with Falconer (except for the similarity in the reaction, but that doesn't make much of a synergy). Falconer, as a gainer, is a card that's better to get early. I always thought Falconer seemed weak for $5, and putting Goshawk on top doesn't help it much.
Treasure Vault (by silverspawn)
$2 - Treasure
You may discard an Action card for +$4.
(on top of King's Court)
I probably had a poor choice of assignment for this contest. I didn't foresee that about half the entries would use official cards that I don't like playing with, and that makes it harder to judge. Anyway, I do think this card might improve King's Court games, both by making it easier for both players to spike $7 (so the first person to spike it doesn't run away with the game), and by making there be fewer King Courts in the pile...
semiFINALIST
Outriders (by Mahowrath)
$3 - Action - Duration
+1 Card
+1 Action
At the start of your next turn, if this is still in play, +2 Cards
-
Discard this from play when another player buys a card with at least $2 unspent.
(on top of Outpost)
I get the idea that this'll give you a five card hand for those Outpost turns, but I think this will be too strong in the early part of the game when people aren't producing a lot of coin every turn. Considering its early game strength, Outriders will probably go empty pretty quick, so Outpost isn't weakened much by having it there. Like with Mystic, I think there are enough ways to take good advantage of Outpost without it having a synergy in the same pile.
Art Colony (by emtzalex)
$2 - Action
+1 Card
You may play an Action card from your hand. If you did, reveal the top card of your deck. If it's an Action costing less than the card played, play it.
(on top of Artisan)
I really like how this card works together with Artisan, and as Art Colony is a cheap cantrip, it shouldn't be much trouble to uncover the Artisans. This is my favorite of the entries that go on top of official gainers. Also, since Artisan costs $6, you might not be able to get it real early anyway, so I don't mind putting another card on top of it as much.
FINALIST
Farmer (by The Alchemist)
$4 - Action
+1 Card
+1 Action
You may discard a Victory card for +1 Card and +$1.
-
When you Trash this, +$2.
(on top of Farmland)
This looks a lot like (the updated version of) Land Survey, but Farmer is more like Shepherd. Shepherd is a strong card. This has the limitation that you can only discard one victory card per Farmer you play for the benfit, but the benefit is even stronger than Shepherd for one victory card, and this is still a cantrip if you draw it without a victory card, unlike Shepherd. Also, I don't like the idea of putting a card on top of Farmland. It doesn't need a nerf, and it's fun to Farmland an Estate into a good $4 card and still have plenty of Farmlands left in the pile to turn your Farmlands into Provinces.
It's hard to choose from the few finalists, but I think I'll go with...
Stablehand by
spineflu as the Winner
...which proves that just because I don't have a lot to say about a card doesn't mean I don't like it.
Runners up:
Art Colony by emtzalex
Destitute Village by JW
Honorable mention:
Vanishing Coin by anordinaryman. Would've been a finalist if it went on top of Venture instead of Adventurer.