Mirror duel is a deck made to fight an identical copy of itself. It cares about all graveyards, powering your spells based on everything cast by you and your opponent.
Knowing what your opponent has in their hand is useful, for cards like Runeflare Trap and Lightning Storm are dangerous spells to play around. The creatures in the list are both sources of damage and ways of manipulating hand knowledge and the graveyard. They are also a target for burn spells, so games may take longer to end without a massive Kindle to the face.
In this environment, card draw is advantageous but risky, since there are ways of punishing both greedy draws and big hands.

The cards
• Augury Adept is a way to regain health, as well as a card draw source without enabling Runeflare Trap or raising the damage from Cerebral Vortex. However, it reveals whatever you're getting to your opponent.

• Izzet Chemister is a tool to control the cards in the graveyard. It allows you to recast your spells again, while running the risk of getting it killed and just losing them. It survives the first Kindle cast in the game, an importat "dies to bolt" metric I consider when deciding on creatures for this list.

• Lore Broker is an instant way to toss stuff in the graveyard and powering up your spells as a surprise. It enables a forceful Runeflare Trap and increases the damage from Cerebral Vortex. It also rotates your hand, if your opponent has knowledge of what you currently have.

• Kindle is the premium damage to the face and removal from the list. It kills all creatures from the get go, with the exception of Izzet Chemister, who is safe until another Kindle is in a graveyard.

• Accumulated Knowledge is a staple. It draws cards based on the amount of cards with its name on any graveyard, so it was a no-brainer to add it here. However, there are spells in this duel deck specifically made to punish it. Accumulated Knowledge is just too good of a card, especially when both players have access to it. It is subpar for the first player who casts it, but gets better as the game goes on.

• Cerebral Vortex is both a card draw source and a damage source. It is a double-edged sword, for if cast on yourself, it helps on enabling a Runeflare Trap, and if cast on your opponent, it can be painful but still give them two cards.

• Lightning Storm is a fun way to use your knowledge of the opponent's hand to your advantage. Dealing a minimum of three, it can very quickly get out of control, calling for a counterspell.

• Rune Snag is a counterspell that perfectly fits the nature of the duel deck. Logic Knot is a counter to aid a control playstyle while also providing a way to power down GY-matters spells.

• Runeflare Trap is one of the most fun cards I've played on the last few years. Seeing an opponent reveal this with Augury Adept makes me IMMEDIATELLY kill off their Lore Brokers and being very aware of everything I'm doing. Originally, I played Trapfinder's Trick to see the opponent's hand without risking taking this to the face, but I preferred cutting this to two per deck and cutting off the trick entirely.

• Baleful Stare and • Psychic Theft are the way of seeing your opponent's hand. You'll draw a few cards from the Stare, but may enable many of the punishes your opponent may have. Theft is a way of getting a tool and hand knowledge while not enabling those punishes, but limiting you to the tools your opponent has in hand.

• Fact or Fiction is a double edged sword, perfect for a game like this. What piles are separated can both help you and your opponent simultaneously, and is an all star here.

Playing a Baleful Stare and seeing a Runeflare Trap on your opponent's hand is worrying. Holding up islands is beneficial to power up a Lightning Storm without powering up a Baleful Stare, but makes it harder to cast Rune Snags or the only current source of lifegain in Augury Adept. There is a balance between dropping your mountains to power down a Stare, dropping your islands to have blue mana to answer spells, playing the tapped lands or holding them for a Lightning Storm. I feel like the tapped duals take away from this, and I'm rethinking the mana base.

Maybeboard
• Frostboil Snarl is a nice upgrade to the taplands. Can be used to gain info on your opponent's hand and be played tapped to bait an unsuspecting Lightning Storm.

• Fortune's Favor Is a neat interaction tool. Fits the Fact or Fiction niche but with hidden information for its caster, allowing for shenanigans from the opponent.

• Memory's Journey powers down GY-Matters spells, is a cheap instant, targets specific cards and has flashback, but its recast cost is in green. To keep the decision-matters theme, I'm thinking of running Evolving Wilds and a single forest.

• Dakra Mystic allows players a pseudo draw, not enabling Traps, and you decide whether everyone gains hand knowledge//feed GYs. Works as a counterpart for the broker, allowing you to take decisions on the opponent's hand instead of letting them control their hand composition.

• Desperate Ravings is a funny draw effect in this environment. You will draw two cards, but you can discard what you don't mean to. Having flashback is just the cherry on top, allowing a recast from the grave or to discard it now and use it later.

• Spellheart Chimera seems to be a good way to reward actually playing your cards and not just stare at your opponent's face, waiting for them to cast their AK first.

• Unsubstantiate Is a Chimera bandage and a Izzet Chemister reset while still giving you a soft counter and hand knowledge.

Current Research
Augury Adept is a nice card, but favors who's winning a lot. The added hand knowledge is not a really valuable tool for the opponent to keep the card around. It is usually an immediate Kindle target, as it dies for just its base power. Thinking of swapping it for two copies of Dream Fracture and two copies of Memory's Journey.

Bamboozle got cut. Testing two additional copies of Fact or Fiction, maybe swap those for two copies of Fortune's Favor. Kinda inclined to have two copies of each so both decks can be built out of a single playset.

Frostboil Snarl and Frontier Bivouac (or Evolving Wilds and a single forest) are likely to swap out the taplands.

Four copies of Lore Broker seem excessive. It is currently too easy to enable a Runeflare Trap. I'm reducing it to two copies and adding Dakra Mystic on their place.

Trade Routes has interesting effects on this mirror, but I feel like they are more interesting additional rules than cards to be added. Maybe have them as optional rules, like emblems, that may be added to the battlefield for both players before the game begins.

How is it playing?

Games still resolve to a state where players are not doing anything, being afraid of counters and waiting to have more lands. When everyone has the resources, the game ends quickly. I am looking to play against more opponents and see if this holds true with different playstyles.

Cutting Augury Adept seems to be the correct choice, since a game with no healing makes every single damage point count.

Memory's Journey is both a way to reset your opponent's graveyard and allow you to reuse your assets in the future. It is a very good card here.

Maybe the correct choice is to swap Psychic Theft for Vision Skeins and leave hand information for the Stare, FoF interactions and player skill.

Updates
Update #1
Swapped Pardic Firecat and Flame Burst for Kindle, Logic Knot and Cerebral Vortex.

Decks played too much like a burn mirror, and I wanted a slower game. The Firecat and Bursts went on to cause heaps of damage, and games ended way too quickly.

Update #2
Swapped 2 Cerebral Vortex for 2 Psychic Theft
Swapped 2 Baleful Stare for 2 Fact or Fiction

Vortex was helping with ending games much quicker than I wanted, and I intend on allowing a game heavy on back and forth with this deck. Theft shall help on the control suite, allowing you to remove a resource from your opponent, using it to yourself and gaining knowledge on their hand.
FoF is a better interaction tool, allowing for more gas to the hand and maybe allowing the opponent to gain some advantage as well, if something nice hits the graveyard. Games are much slower and more interactive now.

Swaps
"I don't like X card"
"Y card is too expensive"
"I can't find Z anywhere near me"

Those are all fair points. I have compiled a list of any similar cards I could find and can fit in, somehow.

Lightning Storm
» Chain Lightning: Seems like a perfect fit, but you'll lose on the holding lands part of the mirror. The objectively correct choice is to just drop more land in an environment without the Storm, making counter wars with Rune Snags easier to deal with.

Runeflare Trap
These suggestions all do the same effect, but you'll lose on the consequences for excessive card draw.
» Sudden Impact
» Gaze of Adamaro
» Toil // Trouble: 2R, but sorc. No gotcha moments.

Kindle
» Flame Burst: The same exact card, but with a different name and able to scale further with Pardic Firecat. If you intend on swapping, I'd recommend to swap all eight copies of kindle for this.

Memory's Journey
» Learn from the Past: Less decisions to be made and double the mana, but can fit.

Logic Knot
» Circular Logic: Still takes advantage of big graves, but cuts out the grave as a resource theme that the Knot allows.

Old cards
The following is a list of cards that were considered or have been used on the list, but got cut for a reason or another. Keeping them here for the future, in case I feel like running them again, or suggestions, if you want to fork this deck for yourself but change a thing or two.

Learn from the Past
Clear the Mind
Steam Augury
Pardic Firecat
Flame Burst
Bamboozle
Arcane Denial
Deprive
Circular Logic
Vision Skeins
Gush
Trade Routes
Mystic Retrieval
Psychosis Crawler
Augury Adept
Psychic Theft