W= Win for Deoxys-Speed
L= Lose for Deoxys-Speed
G= Both sides have to guess to win
S Rank
Gyarados-Mega
W/G: Needs Crunch and Taunt to even have a chance, a 50/50 chance, at that.
A+ Rank
Charizard-Mega-X
W/L/G:
W for Deoxys-Speed if Zardx only has attacks/wisp/sub
L for Deoxys-Speed if Zardx has Flame Charge AND an Attack-increasing move
G for both, if Zardx has an Attack-increasing move, but no Flame Charge or other similar move
Charizard-Mega-Y
W: Just Amnesia and hope for no crits, doesn't have to worry about being slower like Deo-D did.
Dragonite
W/G: Deoxys wins vs mono-attacking Dragonite, but has to play guessing games against mixed z-move/setup
Magearna
W: Unless people use max spa Fairium, Amnesia + Taunt + Recover should just win.
G: Including this because max spa is the most used spread, but I can't say I've ever seen max spa fairium, despite that-
Metagross-Mega
W: Needs to get a crit or enough atk boosts to win, which is unlikely.
L: In this case, L also stands for Laser Focus
with bulldoze
Mimikyu
W/L/G:
W for Deoxys-Speed by using Taunt vs Curse sets
minus Curse w/ Z-Shadow Claw, but who uses that
L for Deoxys-Speed vs any set with Shadow Claw. 12 chances at a 1/8 crit is too much to ignore.
G for both if Mimikyu has Swords Dance.
A Rank
Landorus-Therian
L: Landorus has the convenient combination of commonly carrying speed-reducing attacks AND setup
Snorlax
L: Z-Belly Drum is oof
Tapu Lele
W: Taunt and Amnesia wins. Max Spa lele requires some serious rolls to even have a chance, but that's some highkey unlikely odds.
Zygarde-Complete
W/L: Iron Defense and Taunt wins efficiently vs no Bulldoze Zygod, but Bulldoze turns the tables.
A- Rank
Lopunny-Mega
W: Iron Defense and just Iron Defense, really
Magnezone
W: Statistically, they're gonna miss Metal Sound sooner or later
Porygon-Z
G/L:
50/50's vs Scarf between Taunt vs Trick or Amnesia vs Hyper Beam
Gets obliterated by Z-Hyper Beam + Hyper Beam, sadly. You can bulk for it, but then you end up losing out on a lot of Speed.
Additionally, Nasty Plot just adds even more on the guessing aspect.
Slowbro-Mega
W: Unless I calced wrong, Slowbro has a 39.995889166937% chance of landing 1 crit scald after setting up with Calm Mind. You might classify this as likely enough to warrant a G, instead of a W, but by my standards of luck, I would not. It's basically like relying on a Hypnosis miss to beat Gengar.
Venusaur-Mega
W/G: Taunt first to dodge the Leech, and Amnesia to tank the damage, since Sludge can't kill at +0.
The matchup can be slightly muddied if Venusaur runs max spa AND gets a poison using Sludge Bomb vs Taunt, turn 1, but that's a highly specific scenario that I probably shouldn't even have included-