Reading from top down...
This "Enemy" concept is a bit scary in that it will heavily skew the balance of cursing attacks. Also, adding just 10 extra curses means that it doesn't scale evenly through different numbers of players (in 2p, this DOUBLES the number of curses, in 3p, it only increases the pile by 50%). I'll have to see what these Enemy cards do.
Sorcerer's Apprentice -- The action itself already seems pretty strong. Arguably stronger than Lookout, IMO, and it's only $2. Why do I think it is stronger than Lookout? Lookout is non-drawing non-terminal and FORCES you to trash a card, which means that in the late game you sometimes will opt not to play it in case you draw three good cards. Thus Lookout becomes a dead card. But SA here gets around that completely. You have a smaller selection, sure, but you are never forced to trash a card. In fact, you can even draw it into your hand, meaning that you get lots of utility (non-terminal trashing, deck inspection and filtering) without any risk to your deck because you can always just choose the cantrip option. For $2!
The reaction is interesting but too wordy. The synergy with itself is nice.
I would recommend removing the "put it into your hand" option, or maybe the trashing option. For the reaction, I would recommend cutting out the +1 action for the sake of simplicity. This is a $2 card -- it doesn't need to be super flexible.
Sphinx -- This is interesting but I am not so sure about having the Courtyard option. CY is very strong. Since Sphinx is so flexible, I don't think it should have such a powerful choice. The other options are neat. The money option is actually worse than a pure +$2, but it opens up possible synergies with TfB cards. The trashing option is neat because you are forced to gain (probably) weak card.
Junkyard -- Interesting Cellar variant. Not sure how to evaluate it. It *seems* weak to me, except in heavily junked decks. But I am really not sure.
Villager -- Boring, but it's good to have some simple cards in a set. I'd suggest changing it though:
Villager - $4 Action
+2 actions
Reveal the top and bottom card of your deck. Put one in your hand and put the other one on top of your deck.
It's a bit more interesting, I think.
Slum -- Way too weak, especially with the on-gain. I also don't see a particular reason for that Enemy subtype. If you really want to play with this concept, I would suggest trying an on-gain that curses everyone including yourself. It then functions as a kind of attack except you hurt yourself as well... and yet thanks to the action card itself it doesn't hurt you as much as the others.
Battleground -- this is brokenly powerful. All you need to do is amass +Buy and pile on the Copper. Way too strong. Also, there isn't a great reason for the Enemy subtype here either.
Sorcerer -- The duration effect is pretty interesting. I like it. Compare this to other duration cards to make your phrasing a bit more consistent. It should be: "Now and at the start of your next turn: +$1".
Centaur -- Very similar to Spy or Oracle. That's alright. I think it might actually be a bit too strong for a $4 cost, since it gives both +$2 and draws a filtered card. Tough call.
Pegasus -- does a lot of different stuff, so hard for me to evaluate by theorycraft.
Time Machine -- extremely weak, IMO. It is too swingy because it is based on your opponent's strategy AND his luck on that last turn. Plus you don't get to keep the card? OK, it is non-terminal and you get the card immediately, but I don't think that's enough to make the jump up from $3 Smuggler.
Not to mention that this causes huge tracking issues. Normally you can remember what card you took and return it as demanded by the card text. OK. But what happens if, say, you gain a card and then discard it with Cellar? What if you then reshuffle your deck? Do you have to set aside the card you Time Machine'd so that you have it available to return at the end of your turn? Do you just lose track (and yay now you get to keep the gained card)? What happens if you TRASH the card you gained, or set it aside with Island?
Area 51 -- Probably too weak to cost $5. Black Market only costs $3 but it gives you a choice of three AND the cards could be game-changing cards like a Curser on an attackless board, or Chapel on a board with no other trashing, or King's Court, or all other manners of goodness. Area 51 is restricted to $4 cost cards, you get no choice (you just get one at random), and it is a one-shot. It is generally not worth a $5 buy to get a random $4 card. It's probably most viable with Fairgrounds, nothing else really (it would be much worse than Black Market for cobbling together a make-shift engine).
Griffin -- Tough to evaluate. My gut says that it is often very weak, but sometimes very strong.
Cursed Idol --
I just don't like it. Very, very rarely will it be worth it to gain a Curse just for +$1. Oh, it's a Silver+. Hmm... I think that's alright.
Dragon's Hoard -- Seems... OK, I guess? Only works with money strategies though, and there are probably better X's for BMX.
Redo -- One-shot super-Expand for $5. Hm. No idea how strong this is. Probably ridiculous with King's Court.
Dragon -- I don't see a reason for this to have the Enemy type. Since the gain is completely symmetric, this is basically "trash 2 cards" for $5. Very weak. I suppose the Attack type is on there because you can choose to gain junk to attack enemies, but then you're attacking yourself too so it doesn't really hurt them that much. Embassy and Governor can also force your opponents to gain cards, but they aren't attacks.
Minotaur -- Again, I don't see a compelling reason to having the Enemy subtype. Is it +1 Card, +$1 for every player that doesn't reveal a victory card? The wording could be clearer. These things aside, this looks interesting.
Titan -- I imagine this could lead to really long slogs where everyone's decks are full of Curses and Coppers and they're all playing fully-loaded Titans, which in turn ensures that their opponent will also be able to play a fully-loaded Titan. Does not sound fun to me.
Quest -- Does enough that I'm not sure of its strength. Seems interesting.