Shaman -- What is the purpose of the first clause? In most cases, there is no reason a player would want to put a Curse on top of his deck. It's an unneessary choice to offer the players. In general, it seems too weak to warrant a potion cost.
Ranger -- It's alright, not all that exciting. The ordering choice isn't very meaningful most of the time.
Artefact -- Fine. Reminiscent of the popular fan card Hidden Village.
Unicorn -- Wording is very confusing. It can be made clearer. Here is an attempt:
Unicorn
$4 - Action-Duration
+1 action
Now and at the beginning of each turn this is in play: +$1.
---
While this is in play, when you buy a card, reveal your hand and your entire discard pile. If a copy of the bought card is revealed, discard this.
It is simpler to word it as an Action-Duration.
It is swingy. If you draw it at the end of a reshuffle, when everything is in the discard, that's not cool. If you draw it right at the start, before anything has been discarded, this might help you out for 2-3 turns.
In general, it seems quite weak. VP token games aside, you WILL be buying multiples of things. Engine components, high value treasures, VP cards. You will be buying duplicates of things early, middle and late game. That reduces Unicorn to a mere Copper.
Best case scenarios -- Golden Deck where nothing is ever in the discard pile (could be Bishop driven, or maybe NV-Apothecary). Maybe Fairgrounds strategies while you're buying up all the unique cards, though it gets bad when you actually start buying Fairgrounds. Possibly big engines where you draw and play everything so that nothing is in discard or your hand... but then you still need a way keep yourself from accumulating duplicate VP cards, for example.
Eh, it might be fine. It just seems super, super, super niche. Maybe those good scenarios are enough for it.
Seer -- It's a mini-Golem. Seems fine.
Incantation -- Why specify the three basic types? I don't see a reason to do that. Just have it say, "reveal cards from your deck until you reveal a card that shares a type with and costs more than the trashed card". Works pretty much the same, except trashing a Curse will give you a Chancellor effect. I don't see an issue with that.
I wonder how strong this would actually be. Non-terminal trashing is nice, but $3P is expensive. With increased cycling, you will run out of fodder quickly. You do not often want to trash the actions you buy, I think. This is tough to evaluate.
Dragon -- seems fine to me.