In an effort to post more of my decks at the request of others, I present to you an updated version of Praxis Midrange.
This deck is sort of a mixture of Praxis Tokens and Praxis Midrange. It focuses on Praxis Arcanum, which is probably only good in this deck and other very heavily Time-based unit decks. It is, however, very good here, and is capable of taking many of the signature "broken" Praxis Midrange hands of old and going even further. This is otherwise not a particularly inventive deck, and I'll detail why in the "other considerations" section after tips. I put it down recently as it felt bad against FJS and many Rakano hands, but with FJS being nerfed in ~10-12 hours it is worth opening up again. Tonight it pulled around 17-5. This is still relatively untested so craft at your own risk. I have such marked it as a Work in Progress (though really, that statement feels redundant since it applies to almost every deck.)
Tips
1. Praxis Arcanum is a very tricky card to use properly. I find myself using Refresh on my units a lot to help push in damage and create blockers. Putting it on a Grenadin, for example, makes it a 1/4 which can block most Merchant's and Smugglers. You can also put it on a unit you know you're going to put Xenan Initiation on soon in order to potentially keep a unit alive that would otherwise die in a killer attack. Just be careful to not put a unit in range of Display of Ambition if you suspect they have one.
Next, Viper's Bite. This one is also usually fairly simple in usage, but you can do a lot of tricky things to get more usage out of it. Putting it on a Grenadin or Trailmaker is a great way to make a deadly blocker, or make Sandstorm Titan a nightmare. I also have put it on an Auralian Merchant many times only to then put Xenan Initiation on it to make it a 1/5 Deadly Killer. Lastly, if you need to push in the final points of damage, put it on Worldbearer Behemoth to make a Deadly Overwhelm Unit.
Accelerate is the final and easiest to use mode. I probably use this part the most and it's the best part of the Arcanum. If you can, always try to put it on Worldbearer Behemoth (unless you have some obviously better card to put it on.)
The last thing to know about Arcanum is that the static effect—which is actually absurdly powerful and much better than you think it is—affects all your units, meaning the ones that are in your deck. This makes HotV 5 cost when warped off the top. It also makes Grenadin Drone free.
2. This deck has a lot of tokens and leans very heavily on Obelisk, as the combination of the two seems to get the most mileage out of Arcanum while also being the most difficult for opponents to deal with. Just be careful with your Obelisks and don't stack them up if you suspect a bore is coming—play multiples only when you're going in with your alpha strikes, when possible.
3. If your opponent is playing Shadow, try to always keep a grenadin on the field to sacrifice to Vara. Vara gaining deadly is often very costly for you to deal with.
There isn't much more to the deck beyond this. Like Praxis Midrange of the past several sets, it helps to be very good at navigating combat, as that skill requirement gets doubled with the introduction of Praxis Arcanum.
Other Considerations:
I tried Alhed, Ravid, Insect Master, Moonstone Vanguard, and Marisen's Disciple. They were all good in certain spots but not as good in others. I'm honestly not yet sure what is best here, and certainly not sure for our very new upcoming metagame, but I'm sure they are all viable options. I also briefly tried Daraya but didn't like her all that much—she was just too small all the time and felt bad.
I have no idea how good this deck will be in the upcoming days, but its certainly good enough to do well on ladder and will likely only get better with the new patch. Good luck!