Hmm... I'm interested to see how the rest of this works out.

I would think most of the other cards should roughly have their current costs be their decipher costs and have their normal costs be 1/2 or 2/3 of that. Exception being Memory Exploit, which should probably be 3BB and 5BB

This is insane right?

Oooh. Iinteresting. So it can be Tome Scour, or late-game it can be ciphered if you've got something evasive or if you've cleared the board. Probably more potent than Paranoid Delusions even though it costs far more to encipher.

I wouldn't really say it's insane. It's useful in a deck with lots of evasion that can afford to cast a 5-mana aura.

Should perhaps be uncommon, as this plays the role of Dampen Thought in the Kamigawa draft archetype named after it: just one or two copies can work as your finishers in a control/evasion deck. (Dampen Thought was originally uncommon, as it should be; Modern Masters just took it down to common to screw around with draft strategies.) Alternatively maybe this should go down to 4 cards, as if you've got an evasive creature when you cast this you get to effectively copy it straight away.

On the other hand, there's something to be said for playtesting the dangerous version to see if it is insane or not.

Tangentially related: I was trying to think whether any non-mill decks would want this, and realised that it's a pity that (de)cipher is a non-combo with prowess, while sharing a colour with it. That might be an argument for keeping down the amount of prowess in the set.

...I didn't think it was insane, but that might be my evaluation. In terms of being a Mind Sculpt, it's not great unless you have multiples. The next question is would you pay five to mill 10 if all goes well? I don't think so. But I wouldn't cost it lower.

There really isn't a mill deck and this seems more of an ministrategy within strategies, as mill often is in core sets, which is honestly a great thing to have.

As long as we don't need to spend many slots on it, absolutely. The Dampen Thought deck was completely accidental from WotC's POV as I understand it. But it's cool.

Honestly, all it needs is a "junk rare" and the deck is complete, which is awesome since it is really minimal effort. However, when we draft this someone should force this and see how it plays since it needs less copies of this card than normal.

It'll also be good since lot of our rares are universally better than our uncommons, which probably says more about our rares than our uncommons since a lot of our uncommons are insanly good.