Can be 1v1'd if you choose the correct move on their switch-in:
Modest Specs
Basculegion-F (CM or Psychic, requires Psychic) (Psychic requires any hazard to 2HKO)
Leftovers/Scarf
Hydreigon (Aura Sphere)
Iron Treads (CM or Aura Sphere)
Meowscarada (CM or Aura Sphere)
Sandy Shocks (Psychic)
Swords Dance
Scizor (CM or Aura Sphere)
Boots
Tornadus-Therian (CM or Psychic)
Thundurus-Therian (CM or Psychic)
Flame Orb
Ursaluna (Aura Sphere) (Needs to be burned already or have taken chip previously)
Volcanion (CM, requires Psychic)
Choice Band
Weavile (Aura Sphere) (Other sets never 1HKO you)
Requires a specific item, Tera type or an extra turn of setup:
Arcanine-Hisui (Aura Sphere+Occa Berry/Any Tera)
Garganacl (CM+Covert Cloak)
Bulky
Heatran (CM+Occa Berry/Tera Dragon or Water/Another CM)
Offensive
Heatran (CM+Tera Dragon or Water)
Skeledirge (CM+Tera Dragon or Water+Stored Power)
VS
Arcanine-Hisui
252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Arcanine-Hisui: 192-226 (58 - 68.2%) -- guaranteed 2HKO
+1 252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Arcanine-Hisui: 286-338 (86.4 - 102.1%) -- 12.5% chance to OHKO
252 Atk
Arcanine-Hisui Flare Blitz vs. 148 HP / 0 Def
Jirachi: 360-426 (95.2 - 112.6%) -- 75% chance to OHKO
252 Atk
Arcanine-Hisui Flare Blitz vs. 148 HP / 0 Def
Occa Berry Jirachi: 180-213 (47.6 - 56.3%) -- 84.4% chance to 2HKO
252 Atk
Arcanine-Hisui Flare Blitz vs. 148 HP / 0 Def
Tera Dragon Jirachi: 90-106 (23.8 - 28%) -- 91.6% chance to 4HKO
VS
Basculegion-F
252+ SpA
Jirachi Psychic vs. 0 HP / 0 SpD
Basculegion-F: 171-202 (44.8 - 53%) -- guaranteed 2HKO after Stealth Rock
+1 252+ SpA
Jirachi Psychic vs. 0 HP / 0 SpD
Basculegion-F: 255-301 (66.9 - 79%) -- guaranteed 2HKO
252+ SpA
Choice Specs Adaptability
Basculegion-F Shadow Ball vs. +1 148 HP / 0 SpD
Jirachi: 320-380 (84.6 - 100.5%) -- 6.3% chance to OHKO
VS
Garganacl
+1 252+ SpA
Jirachi Aura Sphere vs. 252 HP / 252+ SpD
Garganacl: 186-220 (46 - 54.4%) -- 4.7% chance to 2HKO after Leftovers recovery
+2 252+ SpA
Jirachi Aura Sphere vs. 252 HP / 252+ SpD
Garganacl: 248-292 (61.3 - 72.2%) -- guaranteed 2HKO after Leftovers recovery
+3 252+ SpA
Jirachi Stored Power (140 BP) vs. 252 HP / 252+ SpD
Garganacl: 403-475 (99.7 - 117.5%) -- 93.8% chance to OHKO
0 Atk
Garganacl Earthquake vs. 148 HP / 0 Def
Jirachi: 146-172 (38.6 - 45.5%) -- guaranteed 3HKO
+2 4 Def
Garganacl Body Press vs. 148 HP / 0 Def
Jirachi: 145-171 (38.3 - 45.2%) -- guaranteed 3HKO
VS
Heatran
+1 252+ SpA
Jirachi Aura Sphere vs. 252 HP / 212+ SpD
Heatran: 170-202 (44 - 52.3%) -- guaranteed 3HKO after Leftovers recovery
+2 252+ SpA
Jirachi Aura Sphere vs. 252 HP / 212+ SpD
Heatran: 228-270 (59 - 69.9%) -- guaranteed 2HKO after Leftovers recovery
0 SpA
Heatran Magma Storm vs. +1 148 HP / 0 SpD
Jirachi: 182-216 (48.1 - 57.1%) -- guaranteed 2HKO after trapping damage
0 SpA
Heatran Magma Storm vs. +2 148 HP / 0 SpD
Jirachi: 134-162 (35.4 - 42.8%) -- guaranteed 3HKO after trapping damage
0 SpA
Heatran Magma Storm vs. +1 148 HP / 0 SpD
Occa Berry Jirachi: 91-108 (24 - 28.5%) -- 93.2% chance to 3HKO after trapping damage
0 SpA
Heatran Magma Storm vs. +2 148 HP / 0 SpD
Occa Berry Jirachi: 67-81 (17.7 - 21.4%) -- guaranteed 4HKO after trapping damage
0 SpA
Heatran Magma Storm vs. +1 148 HP / 0 SpD
Tera Dragon Jirachi: 45-54 (11.9 - 14.2%) -- guaranteed 5HKO after trapping damage
+1 252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Heatran: 226-268 (69.9 - 82.9%) -- guaranteed 2HKO after Leftovers recovery
252 SpA
Heatran Magma Storm vs. +1 148 HP / 0 SpD
Jirachi: 218-260 (57.6 - 68.7%) -- guaranteed 2HKO after trapping damage
252 SpA
Heatran Magma Storm vs. +1 148 HP / 0 SpD
Occa Berry Jirachi: 109-130 (28.8 - 34.3%) -- guaranteed 3HKO after trapping damage
252 SpA
Heatran Magma Storm vs. +1 148 HP / 0 SpD
Tera Dragon Jirachi: 54-65 (14.2 - 17.1%) -- 62.2% chance to 4HKO after trapping damage
VS
Hydreigon
252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Hydreigon: 174-206 (53.5 - 63.3%) -- guaranteed 2HKO after Leftovers recovery
252 SpA
Hydreigon Dark Pulse vs. 148 HP / 0 SpD
Jirachi: 254-302 (67.1 - 79.8%) -- guaranteed 2HKO
VS
Iron Treads
252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Iron Treads: 214-252 (66.6 - 78.5%) -- guaranteed 2HKO
+1 252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Iron Treads: 318-376 (99 - 117.1%) -- 93.8% chance to OHKO
252 Atk
Iron Treads Earthquake vs. 148 HP / 0 Def
Jirachi: 294-348 (77.7 - 92%) -- guaranteed 2HKO
252 Atk
Iron Treads Earthquake vs. 148 HP / 0 Def
Shuca Berry Jirachi: 147-174 (38.8 - 46%) -- guaranteed 3HKO
VS
Meowscarada
252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Meowscarada: 214-252 (73 - 86%) -- guaranteed 2HKO
+1 252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Meowscarada: 318-376 (108.5 - 128.3%) -- guaranteed OHKO
252 Atk
Meowscarada Knock Off (97.5 BP) vs. 148 HP / 0 Def
Jirachi: 284-336 (75.1 - 88.8%) -- guaranteed 2HKO
252 Atk
Meowscarada Knock Off (97.5 BP) vs. 148 HP / 0 Def
Colbur Berry Jirachi: 142-168 (37.5 - 44.4%) -- guaranteed 3HKO
252 Atk
Meowscarada Knock Off (97.5 BP) vs. 148 HP / 0 Def
Tera Fairy Jirachi: 71-84 (18.7 - 22.2%) -- possible 5HKO
VS
Sandy Shocks
252+ SpA
Jirachi Psychic vs. 0 HP / 4 SpD
Sandy Shocks: 153-181 (49.1 - 58.1%) -- 98% chance to 2HKO
+1 252+ SpA
Jirachi Psychic vs. 0 HP / 4 SpD
Sandy Shocks: 229-271 (73.6 - 87.1%) -- guaranteed 2HKO
252 SpA
Sandy Shocks Earth Power vs. 148 HP / 0 SpD
Jirachi: 282-332 (74.6 - 87.8%) -- guaranteed 2HKO
252 SpA
Sandy Shocks Earth Power vs. +1 148 HP / 0 SpD
Jirachi: 186-222 (49.2 - 58.7%) -- 98.4% chance to 2HKO
252 SpA
Sandy Shocks Earth Power vs. +1 148 HP / 0 SpD
Shuca Berry Jirachi: 93-111 (24.6 - 29.3%) -- 99.9% chance to 4HKO
VS
Scizor
252+ SpA
Jirachi Aura Sphere vs. 32 HP / 0 SpD
Scizor: 96-114 (33.2 - 39.4%) -- 100% chance to 3HKO
+1 252+ SpA
Jirachi Aura Sphere vs. 32 HP / 0 SpD
Scizor: 144-170 (49.8 - 58.8%) -- 99.6% chance to 2HKO
252+ Atk
Scizor Knock Off (97.5 BP) vs. 148 HP / 0 Def
Jirachi: 234-276 (61.9 - 73%) -- guaranteed 2HKO
252+ Atk Technician
Scizor Bullet Punch vs. 148 HP / 0 Def
Jirachi: 54-64 (14.2 - 16.9%) -- possible 6HKO
VS
Skeledirge
+3 252+ SpA
Jirachi Stored Power (140 BP) vs. 248 HP / 244 SpD Unaware
Skeledirge: 201-237 (48.9 - 57.6%) -- 94.9% chance to 2HKO
0 SpA Unaware
Skeledirge Torch Song vs. 148 HP / 0 SpD
Tera Dragon Jirachi: 46-55 (12.1 - 14.5%) -- possible 7HKO
+1 0 SpA Unaware
Skeledirge Hex (65 BP) vs. 148 HP / 0 SpD
Tera Dragon Jirachi: 114-135 (30.1 - 35.7%) -- 31.5% chance to 3HKO
VS
Tornadus-Therian
252+ SpA
Jirachi Psychic vs. 0 HP / 4 SpD
Tornadus-Therian: 147-174 (49.1 - 58.1%) -- 96.9% chance to 2HKO
+1 252+ SpA
Jirachi Psychic vs. 0 HP / 4 SpD
Tornadus-Therian: 220-259 (73.5 - 86.6%) -- guaranteed 2HKO
252 SpA
Tornadus-Therian Heat Wave vs. 148 HP / 0 SpD
Jirachi: 184-218 (48.6 - 57.6%) -- 94.9% chance to 2HKO
0- Atk
Tornadus-Therian Knock Off (97.5 BP) vs. 148 HP / 0 Def
Jirachi: 126-150 (33.3 - 39.6%) -- guaranteed 3HKO
VS
Thundurus-Therian
252+ SpA
Jirachi Psychic vs. 0 HP / 4 SpD
Thundurus-Therian: 160-190 (53.5 - 63.5%) -- guaranteed 2HKO
+1 252+ SpA
Jirachi Psychic vs. 0 HP / 4 SpD
Thundurus-Therian: 241-285 (80.6 - 95.3%) -- guaranteed 2HKO
+1 252+ SpA
Jirachi Stored Power (60 BP) vs. 0 HP / 4 SpD
Thundurus-Therian: 160-190 (53.5 - 63.5%) -- guaranteed 2HKO
252 SpA
Thundurus-Therian Thunderbolt vs. 148 HP / 0 SpD
Jirachi: 160-189 (42.3 - 50%) -- 0.4% chance to 2HKO
252 SpA
Thundurus-Therian Thunderbolt vs. +1 148 HP / 0 SpD
Jirachi: 108-127 (28.5 - 33.5%) -- 0.3% chance to 3HKO
VS
Ursaluna
252+ SpA
Jirachi Aura Sphere vs. 124 HP / 0 SpD
Ursaluna: 192-228 (44.4 - 52.7%) -- 82.4% chance to 2HKO after burn damage
252+ Atk Guts
Ursaluna Earthquake vs. 148 HP / 0 Def
Shuca Berry Jirachi: 285-336 (75.3 - 88.8%) -- guaranteed 2HKO
VS
Volcanion
252+ SpA
Jirachi Psychic vs. 116 HP / 0 SpD
Volcanion: 147-174 (44.5 - 52.7%) -- 21.9% chance to 2HKO
+1 252+ SpA
Jirachi Psychic vs. 116 HP / 0 SpD
Volcanion: 220-261 (66.6 - 79%) -- guaranteed 2HKO
252+ SpA
Volcanion Fire Blast vs. 148 HP / 0 SpD
Jirachi: 396-468 (104.7 - 123.8%) -- guaranteed OHKO
252+ SpA
Volcanion Fire Blast vs. +1 148 HP / 0 SpD
Jirachi: 264-312 (69.8 - 82.5%) -- guaranteed 2HKO
252+ SpA
Volcanion Fire Blast vs. +1 148 HP / 0 SpD
Occa Berry Jirachi: 132-156 (34.9 - 41.2%) -- guaranteed 3HKO
252+ SpA
Volcanion Fire Blast vs. +2 148 HP / 0 SpD
Occa Berry
Jirachi: 100-118 (26.4 - 31.2%) -- guaranteed 4HKO
VS
Weavile
252+ SpA
Jirachi Aura Sphere vs. 0 HP / 4 SpD
Weavile: 364-432 (129.5 - 153.7%) -- guaranteed OHKO
252 Atk
Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Jirachi: 302-356 (79.8 - 94.1%) -- guaranteed 2HKO
252 Atk
Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Colbur Berry Jirachi: 151-178 (39.9 - 47%) -- guaranteed 3HKO
252 Atk
Tera Dark Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Jirachi: 404-476 (106.8 - 125.9%) -- guaranteed OHKO
252 Atk
Tera Dark Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Colbur Berry Jirachi: 202-238 (53.4 - 62.9%) -- guaranteed 2HKO
252 Atk
Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Tera Fairy Jirachi: 75-89 (19.8 - 23.5%) -- possible 5HKO
252 Atk
Choice Band Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Jirachi: 450-530 (119 - 140.2%) -- guaranteed OHKO
252 Atk
Choice Band Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Colbur Berry Jirachi: 225-265 (59.5 - 70.1%) -- guaranteed 2HKO
252 Atk
Choice Band Tera Dark Weavile Knock Off (97.5 BP) vs. 148 HP / 0 Def
Colbur Berry Jirachi: 300-354 (79.3 - 93.6%) -- guaranteed 2HKO
252 Atk
Choice Band Tera Dark Weavile Knock Off vs. 148 HP / 0 Def
Tera Fairy Jirachi: 101-119 (26.7 - 31.4%) -- guaranteed 4HKO