Interesting abilities on their own, but some concerns about the deck it's going on vs. the environment:

• Hexproof. What sorts of ways will Phyrexian blue have to get around this? Is Phyrexian blue more aggressive than Neurok blue making this under-the-curve creature a mostly poor play, or does it has a couple of removal pieces that either do some sort of edict-bounce or remove hexproof?

• Both of your blue legends read "Draw cards for doing thematic stuff." if I were you - and I'm not, so feel free to ignore this opinion - I'd probably look towards more ways you can separate and define Phyrexian vs. Mirrodin blue. Maybe Kara Vrist's artifact-untap ability makes you Dakra Mystic? Or maybe it gives something unblockable or shroud?

• From what I understand, the "Look at target player's hand" is going to be mostly irrelevant past the first use, and you're really only going to use this to get your artifacts tapped. Since it's something that encourages repeatable use, maybe have something that encourages tapping multiple artifacts? Some effects that instantly comes to mind as Neurok-relevant are:

• Scry 1. (Generic, but hey. It's a duel deck.)
• Tap X untapped artifacts you control: Look at the top X cards of your/your opponent's library. (Do not rearrange them)
• {minor cost maybe}, tap an untapped artifact you control: ~ gains shroud/hexproof until end of turn.

These are just my humble suggestions. I like the theme of the duel decks so far!

"When ~ enters the battlefield, put a progress counter on it, then proliferate."

As you have it now, you have it as a "comes into play as" ability, but that ability can only convey states, not actions. In other words, since proliferate is an action, if you want it to come into play with a counter and then proliferate, the only real option you have is to use an ETB trigger, or split the ability up into two separate lines of text:

~ enters with a progress counter. / When ~ enters the battlefield, proliferate.

I like this card. Seems to be costed just right for its cost (if a little on the weak side; but it's okay, it's a duel deck mythic. Duel decks are traditionally lower on the power level scale so maybe this might be really good in your environment). Repeatable divination is nice, but the only two real comparisons there are for creatures with this ability is Arcanis the Omnipotent and Soul of Ravnica. To me, this falls more on the Soul of Ravnica side; even though you can potentially draw four or more cards per turn with it, it's probably not going to happen unless you go bat crazy with cantrips.

Don't pay too much attention to Vitenka. The Praetors were all huge stompy things - this is two mana cheaper than Jin-Gitaxias's previous card.

However the previous card drew seven cards immediately. This doesn't have an immediate impact on the board beyond being 6/8.

So yes, this text box could and should be quite a bit cheaper (and the P/T a tiny bit smaller to match). At 4UU for a 5/7 or 6/4 this would be fine. (I can see the inclination to give this a high toughness, but remember Jin-Gitaxias, Core Augur was 5/4.)

Bear in mind that as a proliferate-themed legend, this will be compared to Atraxa, Praetors' Voice. At the moment it comes out of the comparison broadly favourable - Atraxa is more combat-themed, this is more card-drawing - but again it wants to be quite a bit cheaper. And probably the cost to draw 3 cards also wants to come down a little bit. The original Jin-Gitaxias draws you lots of cards repeatedly for free, as do things like Damia, Sage of Stone.

Alternatively, if you do want to keep it at 8 mana, it needs to have some immediate impact on the board. Replace the first line with something like "When ~ ETBs, put a progress counter on it, then proliferate three times"?

It costs eight. It omits the words "Win the game".

I lie the idea of proliferate leading into drawing cards. It just needs to be a heck of a lot cheaper so that there's some chance you ever actually get to do it. I'd think something like with this aim wants to be about CMC5. Would need a smaller body, probably, in that case.

How's this?

Didn't the original praetors all have abilities that were "symmetrically" good for and bad for your opponents? Obviously the new incarnations don't have to follow suite, but I don't see why not to as that was rather memorable.

A card proposal scrapped together pretty quickly:

>
> Flash
> If you would draw a card, draw that many cards plus one instead.
> Each opponent can't draw more than one card each turn.
> 2/5

With this you have to break out the microscope; put the card in a slide; adjust the lighting....

Seriously, too many words. Way too many words.

I don't think much of the objection above the. The aim of this is plainly obviously to proliferate. It's kinda "Evolve: Proliferate" really. But, uh, yeah - not quite sure why this costs 9 mana. For that much mana it could have an extra line "Whenever you proliferate, win the game. Twice."

This seems awful. Especially when compared to the original Jin-Gitaxias, Core Augur. With this you have to cast it from hand, then basically cast two spell with cmc 3 or greater (so no 1-cmc cantrips) and then pay and you get to draw two cards. Compare to the original which has none of those restrictions, costs only more, has flash and pretty draws you seven cards immediately while also making your opponents discard their hand if they are unable to remove it. Sure, the original is rather busted, but this is a huuuge downgrade. Consecrated Sphinx seems much better for example. If you want to proliferate a lot, I would rather go with Inexorable Tide.