So, I designed a few examples of these myself. The nature of the Enchantment mechanic (to me) first evokes the tokens from Adventures. Those, by their nature, have to be fairly simple. By contrast, Enchantments add the potential for a bit more complexity:
Mark of Cain • $5 • Action - Night - Enchantment
Trash up to 2 card from your hand or an Action you would discard from play this turn.
Enchant an Action card. When you trash a card, you may play copies of the enchanted card from your hand.
Mark of Cain, in effect, gives copies of the Action card a reaction that lets you play them when you trash a card. It also provides trashing to trigger the effect (but you will need to get more copies of both MoC and the enchanted card).
Shadow Walking • $6 • Night - Enchantment
Look through your discard pile and put up to 3 cards from it onto your deck.
Enchant an Action: Before you play the Action, +1 Card. After you play it, discard a card.
Shadow Walking is the closest to the Adventures tokens, giving one card of sifting. To maximize this, it draws the card before resolving, and discards after.
Like Augie279, I wanted to do a take on Lost Arts:
Arcana • $4 • Action - Enchantment
+2 Actions
Enchant an Action: When you play a copy of the enchanted Action, +1 Action per two copies of it you have in play (round down).
Arcana does not (by itself) turn terminal cards non-terminal, as the first copy you play doesn't give you any +Actions, and if that's all that happens you won't be able to play another copy. However, it can turn cantrips into villages (starting with the second copy you play). It works well with Duration cards as well; as long as you drop one copy (of, for example, Haunted Woods or Enchantress) each turn, on the following turn all your copies will be non-terminal. Also, if you can start each turn with an extra Action (via Barracks or Merchant Camp), you can play the first copy (of, for example, Smithy) terminally and play the rest as non-terminal.
Another use of the enchant mechanic is to use them like a Project, giving some general effect related to the specific card (as Builder_Roberts, BryGuy, and Xen3k did). Like BryGuy, I thought this worked particularly well with Victory cards.
Midnight Garden • $5 • Night - Enchantment
Gain an Estate.
Enchant a Victory card. At the start of your turn, you may discard a copy of that card for +1 Card.
Midnight Garden sets aside one copy of a Victory card (by enchanting it) and lets you sift a second copy at the start of each of your turns. It's on-play ability lets you start sifting your Estates without having to spend a Buy gaining one.
Like Will(ow|iam), I had the idea for a Command card type effect, where the enchanted card could be played later on:
Invocation • $5 • Action - Command - Enchantment
Play each Action card you have enchanted by an Invocation, in any order, leaving them there.
Enchant a non-Command Action card you have a copy of in play.
Invocation ends up working a bit like
the combine effect from Week 38. Here, the enchanted cards are played by other copies of Invocation, making the setting aside a double burden (taking away both the useful Action card and a copy of Invocation) and the limiting the upper strength because of the pile size . There's an added barrier of needing to have the card you want to enchant in play (which both makes it harder to use and makes limits the use of one-shots). On the other hand, the effect can be incredibly powerful. A Smithy and a Village make the other Invocations into triple labs. Tactician + Watchtower + Vagrant gives you 7-8 cards this turn (after you discard your hands) and 5 cards next turn.
This made me think about other ways in which an Enchantment card might be more about the on-play effect, with the Enchantment ability supporting the on-play (rather than it working the other way around):
Telekinesis • $5 • Action - Enchantment
+3 Cards
+1 Buy
Enchant a card: After you play a Telekinesis, you may discard a copy of the enchanted card for +1 Action.
Telekinesis is a terminal draw card. You can use it to enchant cards (particularly junk card), holding them out of your deck. If you do, you can discard other copies of the card to make Telekinesis non-terminal.
When you do something with a card that could instead be done with a landscape (e.g. a Hireling style "at the start of each of your turns" card instead of a Project), one question that could be asked is "why a card?" With Enchantment cards, one answer can be their on-play ability. Another option (as czzzz realized) is to make Victory cards:
Albatross • $4 • Victory - Enchantment
Worth 3VP if you have a copy of the card this is enchanting in play at the end of the game.
Enchant a Duration. When you play a copy it, choose one: +1 Action; or +1 Buy.
I wanted my Victory - Enchantment cards to have their VP value be tied to the card they were enchanting, giving the ability a double impact. Albatross (good luck for sailors) enchants a duration, making other copies non-terminal (or a source of +Buy). And if it is "in view" of the Duration (e.g. the Duration is in play) it is worth VP.
Magic Keep • $5 • Victory - Enchantment
Worth 5VP if you have more copies of the card this is enchanting than each other player, or tied for most.
Enchant a non-Victory card. When another player plays an Attack card, you may first discard a copy of the enchanted card from your hand, to be unaffected by it.
Magic Keep turns copies of the card you enchanted into weak Moats (which have to be discarded to avoid an attack). It also gives you the Keep VP bonus for that card.
As with Invocation / Telekinesis, there's the possibility that Victory card is the main point, and the Enchantment is harmful or neutral.
Lucre • $4 • Victory - Enchantment
Worth 1VP per differently named Treasure you have enchanted by a Lucre.
Enchant a Treasure: when you play a copy of that Treasure, +1 Buy and discard a card.
You probably don't want Lucre on all of your Treasures. While it gives both a bonus (+1 Buy) and a penalty (discard), and while you may have some dead cards (Actions you couldn't play or Victory cards) to discard during your Buy phase, eventually you'll end up discarding other Treasures you could have played for value that turn. On the other hand, each Treasure you enchant makes each copy of Lucre worth more VP, whether or not that copy is enchanting anything. Also, you don't need any additional copies of the card in your deck to get the benefit, so if you're planning to trash all of your Coppers anyway, you can enchant one gained from the Supply to boost the VP value of others. This also works with Kingdom cards you don't particularly want, or that you only want one copy of (as, unless you're playing with Night cards, the last Treasure you play does no harm from making you discard).
Sister City • $4 • Victory - Enchantment
Worth 2VP if enchanting or enchanted by a Sister City (otherwise worth 0%).
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Enchant a Sister City.
Sister City takes some of these ideas a step further. All it does is Enchant copies of itself, having no other effect than to keep them out of your deck. It ends up being a bit of a Distant Lands variant, giving you 4 VP if you get it out of your deck, but instead of gaining an Action at $5 and playing it, you have to gain a Victory card at $4 and then gain another with it in your hand. (This card doesn't really meet the mechanic that well, and I'd not have judged it positively as a submission.)