Summary of everything I know about the constructed rating system first. (Edit 6/16/22: Mythic Limited appears to be exactly the same) Details of newly-discovered things below that.
- Bo1 K in closely matched Mythic-Mythic matches is 20.37. The “K” for Mythic vs. non-Mythic matches is 20.41, and 20.52 for capped Mythic vs. Mythic matches (see #2). These are definitely three different numbers. Go figure.
- The minimum MMR change for a Bo1 win/loss is +/-5 and the maximum change is +/-15.5
- All Bo3 K values/minimum changes are exactly double the Bo1 K values.
- Every number is in the uncanny valley of being very close to a nice round number but not actually being a nice round number (e.g. the 13 below is 13.018).
- Every match between a Mythic and a Diamond/Plat (and probably true for Gold and lower as well) is rated *exactly the same way* regardless of either the Mythic’s MMR or the non-Mythic’s MMR. In Bo1 +7.4 points for a win and ~13 points for a loss (double for Bo3)
- As of November 2021, all draws are +/- 0 MMR
- Glicko-ness isn’t detectable at Mythic. The precalculated/capped rating changes don’t vary at all based on number of games played, and controlled “competitive” Mythic matches run at exactly the same K at different times/on different accounts.
- Mythic vs. Mythic matches are zero-sum
- MMR doesn’t drift over time
- MMR when entering Mythic is pretty rangebound regardless of how high or low it “should” be. It’s capped on the low end at what I think is 1400 (~78%) and capped on the high end at 1650 (~92%). Pre-December, this range was 1485-1650. January #1500 MMR was 1782.
- Having an atrocious Mythic MMR in one month gets you easier matchmaking the next month and influences where you rank into Mythic. [Edit: via the Serious Rating, read more here]
- Conceding during sideboarding in a Bo3 rates the game at its current match score with the Bo1 K value. (concede up 1-0, it’s like you won a Bo1 EVEN THOUGH YOU CONCEDED THE MATCH. Concede 1-1 and it’s a 0-change draw. Concede down 0-1 and lose half the rating points). This is absolutely batshit insane behavior. (edit: finally fixed as of 3/17/2022)
- There are other implementation issues. If WotC is going to ever take organized play seriously again with Arena as a part, or if Arena ever wants to take itself seriously at all, somebody should talk to me.
MMR for Mythic vs. Non-Mythic
Every match between a Mythic and a Diamond/Plat (and probably Gold and lower as well) was rated *exactly the same way* regardless of either the Mythic’s MMR or the non-Mythic’s MMR. In Bo1 +7.4 points for a win, ~13 points for a loss, and -5.6 points for a draw**(??!??!). Bo3 values were exactly double that for win/loss.
That’s not something I was expecting to see. Mythic MMR is not a separate thing that’s preserved in any meaningful way between months, so I have no idea what’s going on underneath the hood that led to that being the choice of implementations. The draw value was obviously bugged- it’s *exactly* double the loss it should be, so somebody evidently used W+L instead of (W+L)/2. **The 11/11/2021 update, instead of fixing the root cause of the instant-draw bug, instead changed all draws to +/-0 MMR and fixed the -5.6 point bug by accident.
That led to me slightly overestimating Bo3 K before- I got paired against more Diamonds in Bo3 than Bo1 and lost more points- and to my general confusion about how early-season MMR worked. It now looks like it’s the exact same system the whole month, just with more matches against non-Mythics thrown in early on and rated strangely.
Ranking into Mythic
Edit: Read this
Before it got changed in December, everybody ranked into Mythic between 1650 and 1485 MMR, and it took concerted effort to be anywhere near the bottom of that range. That’s roughly, most months, an MMR that would finish at ~83-93% if no more games were played, and in reality for anybody playing normally 88-93%. The end-of-month #1500 MMR that I’ve observed was in the 1800s before November, ~1797 in November, ~1770 in December, and ~1780 in January. So no matter how well you do pre-Mythic, you have work to do (in effect, grinding up from 92-93%) to finish top-1500.
In December, the floor got reduced to what appears to be ~1400, although the exact value is unattainable because you have to end on a winning streak to get out of Diamond. An account with atrocious MMR in the previous month that also conceded a metric shitton of games at Diamond 4 ranked in at ~1410 under the new system. The ceiling is still 1650. These lower initial Mythic MMRs are almost certainly a big part of the end-of-season #1500 MMR dropping by 20-30 points.
Edit: Read this, section is obsolete now.
MMR is preserved, at least to some degree, and there isn’t a clearly separate Mythic and non-Mythic MMR. I’d done some work to quantify this, but then things changed in December, and I’m unlikely to repeat it. What has changed is that previous-season Mythic MMR seems to have a bigger impact now. I had an account with a trash MMR in January make Mythic in February without losing a single game (finally!), and it still only ranked in at 1481. It would have been near or above 1600 under the old system, and now it’s ranking in below the previous system’s floor.
I hope everybody enjoyed this iteration, and if you’re chasing #1 Mythic this month or in the future, it’s not me. Or if it is me, I won’t be #1 and above 1650.