The first month of series 13 is over and the ladder has reset, and I'm happy to report I was able to sneak into Doubles Masterball tier a couple of days ago and get the Master Rank Ribbon onto two Marshadow. I got the first ribbon with 33 W and 18 L and rank of 2206, and then lost a bunch of matches trying to get the second ribbon :P, ending with 34 W 21 L and a rank of 3948.
Didn't end up having time to get it onto any other mythicals, not sure if I'll try to get into Masterball tier again this month.
The team I built was a slight variation on
this team by NielVGC.
The only real changes were that I opted for a weakness policy charizard after its performance at worlds, and I added stealth rock to Groudon. Yes, yes, I know the common wisdom is that no one runs stealth rock in VGC formats because opponents switch less, but it looked like there was a lot of incin intimidate / rillaboom fake out cycling in Series 12 and Charizard looked like it might be popular in series 13, so wanted to see first hand how well it would or wouldn't work. I found that incin and rillaboom were a lot less common this format, so it wasn't as impactful as it might have been in Series 12, but there were at least a few games where it came in handy. That's not to say it wouldn't have been overall better to swap it out to a different move, but it at least wasn't entirely useless and in a Bo1 format probably caught at least a couple of opponents off guard.
I didn't end up tweaking the time at all while I played, but if I did I probably would have swapped in protect over sub on Zacian, as I very rarely got mileage out of sub. I am also torn between thunder wave and scary face on Grimmsnarl. On balance, I think RNGesus blessed me more than cursed me using thunder wave, as there were definitely a few games I would likely not have won without parahax, compared to games I might have lost because t-wave missed. I also considered changing to thundurus or whimsicott to try and improve the speed control of the team, but ultimately didn't because I valued Grimm's screen support too much to switch to Whims, and... I dunno, I liked foul play I guess?
I wish I could say I brought Marshadow to a majority of the games, but the sad fact is the power level of the format made it difficult to reliably use it, especially when a lot of teams had Yveltal or other threats where I thought bringing my other restricted made more sense. I wish we'd had a season or two where mythicals were allowed but other restricted were banned.
However, I definitely did use Marshadow quite a bit, and it certainly earned its Master rank ribbon.
Random highlight: completely outplayed a Magearna + Riolu player trying to set up trick room by effectively using Grimmsnarl to get in t-waves before copycats, which then did not work on Grimmsnarl because of dark immunity to prankster.