S

Charizard-Mega-X
Loses to Rock Tomb + Z-Roar of Time

Dragonite
Loses to Icium Z Blizzard or Will-O-Wisp + Ice attack
S-

Charizard-Mega-Y
Loses to Electrium Z Thunder, Rockium Z Rock Slide, or Calm Mind/Rain Dance + Rock Tomb

Gyarados-Mega
Loses to Electrium Z Thunder or Nasty Plot + Thunder

Magearna
Wins unless Darkrai has Substitute + Spite (+ Leftovers)
A+

Gardevoir-Mega
Loses to Poisonium Z Sludge Bomb

Greninja
Loses to Electrium Z Thunder (or Timid CM)

Metagross-Mega
Loses to Darkinium Z Dark Pulse or Will-O-Wisp

Porygon-Z
Loses to bulky Calm Mind Z Dark Pulse

Tapu Lele
Loses to Poisonium Z Sludge Bomb

Zygarde-Complete
Loses to Ice Beam, Icium Z Blizzard, Z-Roar of Time
A

Meloetta
Loses to Darkinium Z Dark Pulse

Slowbro-Mega
Loses to Dark Pulse

Victini
Loses to Dark Pulse

Zeraora
Wins unless Darkrai has mixed bulk/atk Sucker Punch
A-

Aegislash
Loses to Dark Pulse

Heatran
Loses to Calm Mind + Focus Blast

Kommo-o
Loses to Icium Z Blizzard

Landorus-Therian
Loses to Icium Z Blizzard

Magnezone
Wins unless Darkrai has SpDef Snarl or Substitute.

Mawile-Mega
Wins unless Darkrai has Will-O-Wisp + Disable + Hidden Power [Fire]

Primarina
Loses to Poisonium Z Sludge Bomb

Serperior
Loses to Poisonium Z Sludge Bomb or Icium Z Blizzard

Tapu Fini
Loses to Poisonium Z Sludge Bomb
B+

Aggron-Mega
Loses to Will-O-Wisp

Altaria-Mega
Loses to Poisonium Z Sludge Bomb

Celesteela
Loses to Electrium Z Thunder

Clefable
Loses to Poisonium Z Sludge Bomb

Crustle
Wins unless Darkrai has PhysDef Wisp (or Taunt/QA/Sucker vs SSmash)

Donphan
Loses to Will-O-Wisp

Garchomp
Loses to Ice Beam, Icium Z Blizzard, Roar of Time

Genesect
Wins unless Darkrai has HP [Fire] or Incinerate

Incineroar
Loses to Focus Blast

Porygon2
Loses to Focus Blast (or CM/Plot/Taunt)

Sableye-Mega
Loses to Nasty Plot

Togekiss
Loses to bulky Poisonium Z Sludge Bomb, Icium Z Blizzard, or Electrium Z Thunder

Tyranitar-Mega
Loses to Focus Blast

Volcarona
Wins unless Rockium Z Rock Slide

Venusaur-Mega
Loses to Nasty Plot
B

Ambipom
Loses to Z-Dark Pulse or Focus Blast

Blaziken-Mega
Wins unless Z-Psychic + Substitute

Carracosta
Loses to Quick Attack or Sucker Punch

Diancie-Mega
Wins unless Specs HP Steel

Hoopa-Unbound
Loses to Disable

Jirachi
Loses to Dark Pulse

Kartana
Loses to Dark Pulse

Lopunny-Mega
Wins unless Scarf Focus Blast

Manaphy
Loses to Electrium Z Thunder

Naganadel
Loses to Icium Z Blizzard or Z-Roar of Time

Necrozma
Loses to Dark Pulse

Pinsir-Mega
Loses to Rock Tomb, Icium Z Blizzard, or Electrium Z Thunder

Registeel
Loses to Nasty Plot

Scizor-Mega
Wins unless Choice Specs HP Fire/Incinerate

Tapu Bulu
Loses to Poisonium Z Sludge Bomb or Icium Z Blizzard
B-

Aggron
Loses to Will-O-Wisp

Archeops
Wins with Scarf unless Choice Scarf Darkrai

Audino-Mega
Loses to Poisonium Z Sludge Bomb

Deoxys-Speed
Wins unless Choice Scarf Darkrai

Diggersby
Loses to Max Speed Focus Blast Darkrai (Scarf hits 382 vs Darkrai's 383)

Ferrothorn
Loses to Focus Blast

Golem
Loses to Will-O-Wisp

Haxorus
Loses to physically bulky Icium Z Blizzard or Z-Roar of Time
252 Atk Haxorus Superpower vs. 80 HP / 200 Def Darkrai: 254-300 (84.3 - 99.6%) -- guaranteed 2HKO
252+ Atk Haxorus Superpower vs. 144 HP / 248 Def Darkrai: 268-316 (84.5 - 99.6%) -- guaranteed 2HKO

Heracross-Mega
Wins unless Flyinium Z Aerial Ace

Jumpluff
Loses to any Ice attack

Krookodile
Loses to Icium Z Blizzard

Kyurem
Loses to Rock Tomb + Z-Roar of Time

Latias-Mega
Loses to Dark Pulse

Magneton
Wins unless bulky Snarl

Medicham-Mega
Loses to Z-Dark Pulse

Nihilego
Loses to Calm Mind + Dark Pulse

Pheromosa
Wins unless Choice Scarf Psychic/Aerial Ace Darkrai

Quagsire
Loses to Taunt

Sawk
Wins with Choice Scarf

Swampert
Loses to Taunt/Wisp/CM/DarkZ

Terrakion
Wins with Choice Scarf

Type: Null
Loses to Taunt

Vivillon
Loses to any Ice attack

Whimsicott
Loses to Poisonium Z Sludge Bomb, Icium Z Blizzard + Taunt

Zapdos
Loses to Icium Z Blizzard

Araquanid
Loses to Electrium Z Thunder