As Cocktail basically makes Potion a Gold+ if you connect two of them, it seems a bit unrewarding to me. I'm not as sure here, as the first comparison i can think of is Treasure Map, which only works once and is terminal, but gives a much more effectful reward. Horse Trader also comes to mind, and again has a few disadvantages over Potion (discarding, terminal), but also is much more flexible and has a Reaction.
Graduate seems cool and is easy to get. It's probably the one that works best as a Potion event because it doesn't do too many different things. Unicorn also is pretty easy - but isn't it a bit weak compared to Expedition, even with the +Buy?
I also like the idea behind Transfigure, although there i actually feel it would work better as an Action card. Maybe it's a bit too strong to be able to buy any $5 for just $4 by making the first one (non-terminally) dead. Consider Feast as a comparison, although of course even Feast has an advantage being able to gain VP cards.
While i think that Magic Amulet and Ghost Hunt are cool, i think they do a bit more complex than i would expect from an Event. Ritual is kind of on the edge here for me.
Research, P
+1 Buy
Once per turn: Name a card. When you discard copies of that card from play this turn, you may put them on top of your deck.
I find it funny that Lab+Research is basically the same as an Alchemist stack.
That's the joke