Pinsir-3 (Mega)
This thing’s Thrash hits way too hard, and puts all members of the team in immediate danger since it outspeeds everything. Thankfully it can’t OHKO anything, but crits will. It does more than half HP damage on Scizor, so it’s not the best idea to try to stall to get Pinsir to hit itself in confusion. Fini can live one Thrash, but it definitely can’t switch in on it. I think the best way to beat this thing is to use Drake as soon as any Pinsir comes out, even it turns out to be the significantly less dangerous Pinsir-4.
Articuno-2
It’s hard to deal with Articuno-2. Garchomp can’t set up or use Drake without dying, so I have to swap out. Fini can’t effectively beat Articuno-2 in time before Sheer Cold is used, so the end goal is Scizor. Articuno will always use Ice Beam on the first swapping turn, which carries the 1/10 risk of a freeze on Scizor. I can try to avoid this with Misty Terrain by swapping from Garchomp into Fini into Scizor, but it’s super dangerous for Scizor if Articuno uses Lock-On on the turn that it switches in. I think I’ve had times when Articuno-2 uses something other than Lock-On during the switch from Fini to Scizor, which is good for Scizor, but seems unlikely, and my memory might be bad. If it does use Lock-On on the Fini to Scizor switch, I can always swap back to Fini and let it get KO’d, allowing Scizor get at least one Swords Dance and KO’ing Articuno with Bullet Punch before Sheer Cold gets used. But trading Fini for a +2 Scizor isn’t a trade I like to make. I’m not sure. Hence why it’s hard to deal with Articuno-2.
Gyarados, both sets
While not impressive by themselves, both Gyarados sets can set up with Dragon Dance to great effect. Also, if Gyarados has Intimidate, Garchomp can’t OHKO it with Drake, so Garchomp has to switch out, since it fears Garchomp-3’s Ice Fang. Furthermore, even if Gyarados doesn’t have Intimidate, Drake only OHKOs Mega Gyarados-4 5/16ths of the time. All of this means that Gyarados will almost always live on its first turn, and I’m pretty sure it always goes for Dragon Dance that first turn since Ice Fang can’t OHKO Garchomp. I typically switch to Fini to deal with Gyarados. CM then 2HKO Gyarados-3 with Moonblast, or just 2HKO Mega Gyarados with Moonblast If something does happen to Fini, Scizor might be able to finish off Gyarados-3, or Garchomp can deal with Gyarados-4.
Salamence-4 (Mega)
This thing is scary since it outspeeds and its Double Edge damage is terrifyingly high, although thankfully the potential Intimidate doesn’t matter too often. It carries Dragon Rush which OHKOs Garchomp, and its Double Edge does more than half of Scizor’s HP. Always switch into Tapu Fini, since it will use Dragon Rush on the first turn if it’s Salamence-4, or Fini can set up many CMs against Salamence-3. From here, Salamence-4 will use Double Edge, giving itself lots of recoil, putting itself in range for Moonblast to KO. In scenarios where it crits the Double Edge on Fini, Scizor can use one Swords Dance to have a guaranteed Bullet Punch KO after both instances of recoil. Alternatively, Misty Terrain is up so Garchomp won’t get OHKO’d by Dragon Rush. The AI accounts for this though, and will use Double Edge against a Garchomp in Misty Terrain, which Garchomp can live at full health and use Drake to KO Salamence, but will leave Garchomp at low HP. In other weird situations, Scizor can spam Roost to whittle down Mence with recoil.
Aerodactyl-3 (Mega)
This set carries both Fire AND Thunder Fang, so Scizor and Fini don’t like to stay in against it, and it also outspeeds the team. Garchomp can beat it with Drake and Rough Skin, but takes a fair amount of damage in the process. Against Garchomp, it will always use Sky Drop, against Fini, it will always use Thunder Fang, and against Scizor, it will always use Fire Fang. Aside from using Drake, one way to beat Aerodactyl-4 is first, switch to Fini, and Aerodactyl will use Sky Drop. Sky Drop will go first and Fini should use Surf. Next, swap back to Garchomp so that Thunder Fang does nothing. Next, switch to Scizor, and Aerodactyl will use Sky Drop. Scizor can either Roost or Swords Dance after Sky Drop damages it. Finally, Mega Evolve and finish Aerodactyl off with a Bullet Punch. Unfortunately this particular strategy only works when all team members are alive. On the first turn when the Aerodactyl set is unknown, Fini is still a good switch since it can just Surf against Aerodactyl-4.
Raikou, all sets
Raikou is more annoying than anything else, at least when I’m not paying attention. I like to watch streams while grinding the Tree, so if I’m not paying close attention, I’ll miss both the trainer’s name and the prompt indicating the opponent has an Air Balloon. Even without distraction from important details, Raikou has options that can make it tough to deal with. First of all, it outspeeds everything. There’s Reflect on the Air Balloon’d Raikou-4, Shuca Berry on Raikou-1, and all sets have either Extrasensory or Shadow Ball which damage Garchomp more than I’d like. Fini’s not well equipped to deal with Electric-types, but can usually survive at least one attack and do just under half of Raikou’s max HP with Moonblast if unboosted. Scizor can try to stall and set up, but Paralysis could always happen, whether from Thunder Wave, Thunder, or Thunderbolt. If the set is Raikou-4 (Air Balloon), I’ve decided that switching into Fini, back to Garchomp, to Scizor, Scizor uses Roost until Misty Terrain and Reflect expire, then Brutal Swing on the turn that Raikou uses Reflect. Swap into Garchomp, use Swords Dance and EQ. Unfortunately this means that the opponent is left with a lingering Reflect for one turn, but Garchomp is at +2 Attack. Otherwise, for Raikou 1, 2, or 3, use Earthquake and hope it doesn’t have Shuca Berry.
Gengar, both sets
Both sets outspeed the entire team, and with strong Shadow Balls, both sets having coverage that hit Fini super-effectively, and Gengar-3 having Dazzling Gleam, both sets will at least do moderate damage against any team member. Compounding the problems is there’s no way to know whether it will Mega Evolve until after a move is made. I’ve settled in on letting Garchomp just take a hit and returning an Earthquake for a KO, since it survives every attack both sets can use, assuming no crit happens. Scizor can deal with Gengar reasonably well too, and it switches into Gengar's moves that target Fini perfectly. Might as well set up 1 Swords Dance and Bullet Punch, since Brutal Swing OHKOs and a SE Brutal Swing = +2 Bullet Punch. Unfortunately Gengar is not uncommon thanks to Plumeria.
Metagross-4 (Mega)
It outspeeds everything, hits very hard, and lives Garchomp’s Earthquake. There are a couple of options to deal with it. One is to have Garchomp eat the first-turn Meteor Mash and use Earthquake, leaving both Metagross and Garchomp at low health. If Garchomp stays in it's a double-KO because of Rough Skin. Alternatively, swap to Scizor after Garchomp’s Earthquake. Unfortunately it usually uses Meteor Mash here since it usually doesn't roll high enough to prefer Bullet Punch. If Metagross didn't get an Attack boost, congrats, it's setup fodder. Against Scizor, Metagross will always spam Brick Breaks, and Scizor can then very safely use Roosts and work its way towards Swords Dances and a Bullet Punch, even if Brick Break crits. Even if Garchomp faints to a crit, Scizor can set up just the same. In the worst cases, any given Meteor Mash has an 18% chance of getting an Attack boost on the turn Garchomp uses Earthquake or when Scizor has to switch into a Meteor Mash. Scizor can still set up since +1 Brick Breaks do less than half HP damage, but the potential for crits make this situation scary. Any +2 or better Bullet Punch will KO after EQ. It's probably best to sac Garchomp and remove Metagross if it gets the turn 1 Attack boost, unfortunately. For other options, Scizor can just switch into a Metagross blindly but things can go bad if it's the Mega set and it gets the Attack boost since it's not at low health.
Alakazam-3 (Mega)
Outspeeds and hits its Focus Blasts way too often. Garchomp can return a Drake after taking a Psychic, but hopefully Garchomp hasn’t taken too much damage already. At full health, Garchomp can live most Psychic crits, so any given Psychic only has a 1.8% chance to OHKO the entire HP bar. Alternatively, Alakazam is a bit of a setup opportunity. Scizor can swap in and PP stall the Focus Blasts, then work its way towards +6 Attack. Just hope that the Focus Blasts or eventual Shadow Balls don’t drop its Sp. Defense, but fortunately Alakazam also likes to use Grass Knots once Focus Blast is done. Scizor can work around -1 Sp. Defense, but it’s better switching to Fini and back to Scizor for safety. Or, Scizor might have used a couple of Swords Dances, and can just Bullet Punch Alakazam once its Sp. Defense gets dicey. +2 Bullet Punch OHKOs Mega Alakazam.
Landorus, all sets
Landorus is surprisingly annoying. Garchomp does outspeed all sets, but the Choice Scarf’d Landorus-2 is an exception. Landorus-1 carries Bright Powder and Fissure, and Landorus-4 has Explosion. Also, any of these sets can hit moderately hard, but Landorus-3 can use Sandstorm, pushing its Earthquakes to dangerously high power, especially if team members have already taken damage. I think Garchomp should always scout Landorus with Substitute. Garchomp can easily set up against Landorus-1, and ignores the Bright Powder with Drake. Against Landorus-2, Garchomp will take an Earth Power, then use Substitute, meaning it can safely use Drake on the next turn. For Landorus-3, ideally it uses Protect, but it also lives an unboosted Drake, so be careful. Landorus-4 would ideally use Explosion, but I think it rarely goes for it turn one. Fini can do decently well against Landorus with Surf, but it can’t always OHKO, and it usually takes a good chunk of damage in the process. Not my favorite option. But at the end of the day, I can’t complain since the Tree holds off from using Landorus-Therian.
Tornadus-1
I’ve never really thought of Tornadus as much of a threat, more so an annoyance that can just get OHKO’d with Drake, until one day this set outsped and OHKO’d Garchomp with its Supersonic Skystrike. Then I started paying attention to it. Turns out this thing has an 81.3% chance to OHKO Garchomp. So if the opposing trainer can carry Tornadus-1, I think it’s best to swap in Fini and let it tank the hit. From there, Tornadus will follow up with a Hurricane, and Fini should use Moonblast. Fini will probably get KO'd by the Hurricane if it hits, so back to Garchomp to use Drake. Sometimes Hurricane will miss or Skystrike and Hurricane low roll and Fini will live, in this case Moonblast again. Either Fini will KO Tornadus, or Scizor gets a free switch. For the other sets, Garchomp can just use Drake, or use the above strategy and have Fini deal with Tornadus; she matches up a little better when she's not taking a Z move.
Togekiss, both* sets
*(Perri’s Togekiss-2 doesn’t count)
The biggest pitfall with this opponent is the idea that Scizor can swap in and set up against another Fairy-type. The 1/3 chance that Togekiss can have Serene Grace boosting its Air Slashes to a 57% flinch rate means that it’s far too dangerous for Scizor to try setting up. Even if it has one of its other abilities 2/3rds of the time, it can still get flinches just the same. Garchomp can’t touch this thing, and it outspeeds Fini, so Scizor is the main option, unless Fini has some CM boosts and doesn’t mind taking a hit or two. I like to just switch into Scizor and use two Bullet Punches to deal with Togekiss.
Arcanine, both sets
Garchomp normally deals with Arcanine with its Earthquake, but if it has Intimidate, Garchomp can’t OHKO it. As a Water and Fairy-type, Fini wants to swap in against Arcanine-4 since it’s a Fire-type that likes to use Close Combat and All-Out Pummeling, but it wants to avoid Arcanine-3 since it always goes for Sunny Day on the first turn and carries Solar Beam. I’ve found that using Swords Dance against Intimidate Arcanine works well if Garchomp is at full HP. Arcanine-4 also carries Extreme Speed, which can definitely catch me off guard if I’m not thinking about it, especially with how much damage it can do against Garchomp (23.4 - 27.8%). Also, pay attention to the trainer name since many of the sun team trainers only carry the Sunny Day set; it doesn't have to be a coin flip and Swords Dance is best for these.
Noivern, both sets
Noivern can be easily dealt with by switching into Fini and using an unboosted Moonblast, but if Fini already fainted it’s very tricky for Garchomp and Scizor to deal with. And even though Fini answers Noivern, Noivern-3 could still makes things annoying by getting one or two Air Slash flinches. Noivern outspeeds Garchomp, and both sets pack Flamethrower and Dragon Pulse. Flamethrower has a 6.3% (10.2% including crit) chance to OHKO Scizor, but it’s not like living one Flamethrower is going to do much good, because the best bet is for Scizor to use two Bullet Punches and pray that one of them crits. Dragon Pulse does (83 - 98.3%) damage against Garchomp, so hope that Garchomp hasn’t taken any damage this battle, or that a crit doesn’t happen. If Misty Terrain is still up when Garchomp switches in, then it has a much better chance to make a comeback.
Whimsicott-3
This set is more of an annoyance than a threat. But since it’s a Fairy-Grass-type, it shouldn’t even be a problem; Scizor can just set up on it, right? Sure, but it’s slow and painful to do so, since Whimsicott-3 carries priority Cotton Guard so it’s like Swords Dances do nothing against it. Throw in priority Substitutes and Leech Seed, and this thing becomes a slog to work around. It’s such a juxtaposition to how easy Whimsicott-4 is to deal with. But it turns out that Whimsicott has fairly below-average HP and Sp. Defense, and Whimsicott-3 doesn’t have an attacking Grass move, so some combination of Scizor’s Bullet Punches and Fini’s Moonblasts easily gets around this thing.