Yeah, it's incredible against Thespian's Stage , Vesuva , Maze of Ith , Mystifying Maze , and paired with tabernacle it's baller.

Decree of Annihilation ?

Grand Arbiter Augustin IV

Does Chancellor of the Annex count?

Theophilus Chancellor of the Annex is there

I have a list of a few cards which might fall under this heading.

Feroz's Ban increases cost of creatures

Imi Statue slows down artifact ramp

Lodestone Golem spells cost more

Null Rod prevents artifacts activated abilities (including mana abilities)

Omen Machine shuts down heavy draw decks

Orb of Dreams slows down all decks negates haste as well as mana ramp

Sands of Time not sure if this fits, but can potentially slow decks down

Torpor Orb etb effects no longer work

Tsabo's Web shuts down utility lands as pointed out in a previous comment

Fatespinner slows down decks by making people skip phases

Jin-Gitaxias, Core Augur not sure if it fits as primary use is draw 7, but if it sticks limits hand sizes

Kira, Great Glass-Spinner not sure if it fits, but it can be used to protect your creatures to a limited degree

Llawan, Cephalid Empress blue creatures cant come down, might be too limited not sure

Platinum Angel not sure but prevents-ish people from winning

Teferi, Mage of Zhalfir says no to counter decks as well as general responses, combos with omen machine

AEther Barrier creatures cost more

Arcane Laboratory slows down many decks

Dismiss into Dream not sure but shuts down enchantment/equipment heavy decks as well as bounce and other targeted spells turn into Murder

Energy Flux hurts artifact heavy decks as well as making turning Sol Ring and Mana Crypt into Darksteel Relic

Frozen AEther stuff enters tapped

Mana Maze slows down mono-colored decks

Pendrell Mists another The Tabernacle at Pendrell Vale

Psychic Surgery hurts most tutor reliant decks as most tutor put it on top of the deck

Rising Waters slows down mana development

War Tax a more flexible Propaganda

Words of Wind useful for making slowing opponetnts down.

Hydra Omnivore

Death Cloud and Pox are staples in Stax that had black.

Please remember to check that the card you're suggesting is not already in the list.

Armageddon (along with its snowclone Ravages of War ) is a staple in stax.

Tangle Wire is also widely used in Stax.

Rishadan Cutpurse , Rishadan Footpad and Rishadan Brigand ?

Since Erayo, Soratami Ascendant is banned, you might want to take that out

Erayo is only banned as being the commander, as a part of the deck it is perfectly legal

As of September 12th, Erayo is banned entirely.

Ok, so is this list just not yet updated?

Wizards does not actively regulate and update the banned list. This is the announcement that came out a few days ago.

The forums at mtgcommander.net are usually the way to go for banned list rulings.

AEther Flash and Price of Glory are great effects as well.

Dosan the Falling Leaf seems staxy. It hates on counterspells at the very least

Considering Pestilence is here, I'm surprised its colour-shifted equivalent Pyrohemia isn't.

Is Meekstone considered stax?

Hum of the Radix

Part I:
1. Archfiend of Depravity
2. Basandra, Battle Seraph
3. Eidolon of Rhetoric
4. Fatespinner
5. Gaddock Teeg
6. Glowrider (same as Thalia but for one more mana)
7. Hushwing Gryff
8. Platinum Angel (opponents can't win)

Part II:1. Bedlam2. Blind Obedience3. Cornered Market4. Damping Field5. Equipoise6. Fight or Flight7. Forsaken Wastes8. Hum of the Radix seconded9. Mystic Barrier more troll than group slug but up to you10. Chalice of the Void11. Cursed Totem12. Thorn of Amethyst13. Austere Command14. Supreme Verdict

reformatted for ease of reading
Part II:
1. Bedlam
2. Blind Obedience
3. Cornered Market
4. Damping Field
5. Equipoise
6. Fight or Flight
7. Forsaken Wastes
8. Hum of the Radix seconded
9. Mystic Barrier more troll than group slug but up to you
10. Chalice of the Void
11. Cursed Totem
12. Thorn of Amethyst
13. Austere Command
14. Supreme Verdict