There are some really interesting concepts here, but I think you'll need to iterate over these a lot to land them. Here are some suggestions:
Chemistry $0P Action - Treasure
+1 Buy.
Play an action or treasure from the supply. Trash it when it would leave play. Trash Chemistry. You may gain a potion.
This should be an Event, since having to buy it then trash it slows it down to the point where I wouldn't spend a Potion on it.
Also, you might want to consider capping the targets so players don't just use it on Platinums. Or not.
Seasonal Commision
6$ Treasure - Duration
Worth 3$
When you play this, reveal your hand and trash all Actions in your hand or play area. For each card trashed this way, gain a differently named Action of that cost or less. At the start of your next turn, return Seasonal Commision and each card you trashed this way to the supply and gain a Gold.
I suggest:
Seasonal Commission - Treasure $6
$3
At the start of your Clean-up, exchange each Action you have in play for a differently named Action of equal or less cost, and exchange this for a Gold.
Warning: this still is a great way to make people spend 10 minutes deciding what to do with all their actions. Also, if they have more than one Seasonal Commission in play........
Brewer 3$ Action - Attack
Name a card. If you have one copy of that card on your Tavern mat for each opponent, each opponent gains a copy from your mat. Put any number of cards with that name from your hand onto your Tavern Mat.
My advice on this is totally different: I'd completely rework it to be a card that collects copies of the named card and then puts them into your hand. So something like "Name a card. Put any number of cards with that name from your hand onto your Tavern Mat. Reveal your hand. If your hand contains copies of the named card, put all the copies from your Tavern Mat into your hand." Then playtest it to death to determine what the cost of it should actually be.
Mayor 5$ Victory
Worth 4 VP
_____________
Your provinces are worth 4 VP
This is a fun idea but the problem (other than what other players say) is, why would I buy a Province, then? I guess to end the game? Although perhaps that is the point, to make is so that players buy Mayors and then tries to end the game before the players who buy no Mayors can get a lead. In which case, this is pretty decent, although testing will determine costings.
[Crucible 3$ Action
+1 Card
+1 Action
+1 Buy
_______________________
While this is in play, Silver is worth 1$ more, but when you play a treasure, it's not worth $ if there are more Treasures in play than Crucibles.
I'd do this (warning: phase breaking!) like so:
Crucible - Action $3
+1 Card
+1 Action
+1 Buy
Play a Treasure card
-
While this is in play, Silver is worth +$1, and you cannot play Treasures during your Buy phase.
Normal comment about testing.