Here's a scan through:
Petroglyph - reaction should just be 'When you discard this card during an Action phase, you
can may reveal it and set it aside.'
Probably fine alongside Faithful Hound, this feels good and belonging in the set.
Discovery - I anticipate card space to be difficult here, especially as you'll probably want to add 'until not on top' to shuffling it into a pile. Making it an Action (+1 action + $2) would help a bit, but that isn't thematic. So maybe:
(+1 action +) $2
While this is in play, when you next buy a card, shuffle this into that card's pile until the top card is not Discovery.
-
When you reveal this from a non-Discovery Supply pile, gain it and a Gold.
Technically you'd want to put it in a random place in the pile, but that's something only a computer (or another person who isn't playing) could do. Sure it doesn't actually break the game if you shuffle it into the Castles or a split pile, but some people will take issue with a premature Plunder or a King's Castle on top, so this could only ever be a fan card.
Artifact - maybe, 'While this is in play,
directly after you when you next buy a Treasure, you may discard this to play that Treasure and
get +1 Buy.
Or to save confusion with Venture and potential tracking issues, you could set the Artifact aside (change 'discard this' to 'set this aside' and add 'Discard this at Clean-up' at the end). I can't really see a way to get one card to play one Treasure without implying Throning when you use several Artifacts, though.
Avatar of Greed - only now do I see you can just buy Victories with this and store them on the mat out of the way, very strong on a 4 cost Gold. You could specify non-Victory cards easily enough though.
Digsite doesn't need to be a Victory. I guess this can run into neverending game trouble with Lurker too.
Encroach has a definite feel of too strong about it. Discard a Gold and it's a bit like getting +1 buy + $5 non-terminally, yet you can redraw the Gold later (empty deck, another Encroach would do it). I'm imagining a choose one clause between draw and the discard may make a balanced card.
Archaeologist - maybe, '
Reveal Look at the top 6 cards of your deck. Put 3 of them into your hand,
Choose one: then either discard the remaining cards or put them
onto your deck back in any order.'
Profiteer - just its top part, 'Trash a non-Victory card from the Supply. Cards with the same name as
that one it cost $1 less this turn,
but not less than $0.
Shipwreck - just, 'Look through your discard pile and put a Treasure from it
onto at the bottom of your deck.'
Stronghold - just mentioning that you could reveal it with the Reaction any number of times to trash more than once. It could stay, but maybe it's a bit too potent a trasher like this. If it is, it looks like the Reaction will more or less do the same thing just playing the Stronghold a la Caravan Guard.