Lost Arts is an Event from Adventures. It gives +1 Action to all of your cards from an Action Supply pile.
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Lost Arts produces a +1 Action token, which modifies a pile so that those cards give you personally +1 Action. Each player has their own token. Say you put the token on ; for you, Smithy is +1 Action +3 Cards, but for everyone else, it's still +3 Cards (unless they also put their token on Smithy). For example. So uh there's probably something good you can do with that. That Smithy example doesn't sound half-bad. The token on Smithy affects all of the Smithies you have, and any Smithies you get later; it's just a different card for you. It's like a giant pile of that are always there when you need them for a particular action, for a one-time payment of and a Buy. You are probably wondering, is there also a +1 Buy token, a +1 Card token, a + token? Yes, of course there are those too.