Here's how WotC officially described their latest event, Mirror, Mirror, a slight departure from the expected in order to rebalance 12 previously banned cards:
My main interest in this event is that it provides something that is usually missing for players that enjoy constructing experimental Historical decks — a free play mode that isn't ranked.
That already does exist for Standard. But it would be nice to have a consistent place to mess around with deck ideas and the vast possibilities of Historic, without jeopardizing ones hard won ranking.
That said, Mirror, Mirror provides just such a laboratory for the time being. And I kinda hope it's also a lab in the sense that maybe Wizards will be gauging interest in a more open, standing Historic play mode from participation.
To be honest I've played several decks (mostly White) in Mirror, Mirror over the last few days and have neither used nor come up against any of the rebalanced cards ostensibly at the heart of the event. That's despite it being an all access format where you don't even need to have cards in your collection to use them.
So, I suspect a lot of players are treating this as the missing-until-now Play Historic mode.
Here's the Deck I played in the gameplay video above:
Deck
4 Fountain of Renewal (M19) 235
3 Light of Promise (M21) 25
1 Shadowspear (THB) 236
2 Light of Hope (IKO) 20
4 Banishing Light (THB) 4
1 Rustwing Falcon (M19) 36
4 Battlefield Raptor (KHM) 3
4 Study Break (STX) 34
4 Beloved Princess (ELD) 7
1 Face of Divinity (JMP) 103
4 Charmed Stray (ANB) 5
4 Staunch Shieldmate (M21) 39
4 Star Pupil (STX) 30
1 Charming Prince (ELD) 8
2 Guiding Voice (STX) 19
1 Celestial Mantle (JMP) 96
1 Angelic Reward (ANB) 3
3 Angelic Ascension (M21) 3
2 Candlelight Vigil (GRN) 3
26 Plains (THB) 278
1 Castle Ardenvale (ELD) 238
1 Idyllic Grange (ELD) 246
1 Sejiri Shelter (ZNR) 37
4 Tranquil Cove (M21) 258
4 Scoured Barrens (M21) 250
4 Wind-Scarred Crag (M21) 259
4 Blossoming Sands (M21) 244
4 Thriving Heath (JMP) 35
1 Kenrith, the Returned King (ELD) 303
Sideboard
2 Introduction to Prophecy (STX) 4
1 Expanded Anatomy (STX) 2
1 Environmental Sciences (STX) 1
1 Fractal Summoning (STX) 187
1 Spirit Summoning (STX) 236
1 Elemental Summoning (STX) 183
Some of this work is unofficial fan content permitted under the Wizards of the Coast Fan Content Policy rather than approved/endorsed by WotC. Accordingly, such portions of materials used remain property of Wizards of the Coast.