Gimmigone

Attackers: These guys don't need to tera, but if they do they're going to do a lot of damage.
https://pokepast.es/25eca9a162947e25

Listed in order of effectiveness

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Ursaluna - THE BIG BEAR (Tera Normal/Stellar) - Base typing is perfect, Normal makes Facade absurdly powerful
- Click belly drum
- flame orb activates, guts goes online
- click facade if the enemy isn't Ghost/Rock/Steel
- click headlong rush if the enemy is rock or steel
- win c:

Notes:
Belly Drum raises Ursaluna's attack to maximum immediately at the cost of half of its HP. Flame Orb activates at the end of the turn, which will activate Guts, increasing Ursaluna's attack further by 50%. Facade doubles in power if the user is affective by a status condition (aka that burn from the flame orb). Essentially, you have a lot of multipliers that snowball into insane damage amounts.
+6 252+ Atk Guts Ursaluna Facade (140 BP) vs. 0 HP / 0 Def Tera Flying Gimmighoul: 2127-2503 (920.7 - 1083.5%) -- guaranteed OHKO

Teammates:
Tyranitar is a good partner here, or anything that can learn Screech.

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Azumarill: Silly Rabbit (Tera Water/Stellar) - Water to boost Liquidation
- Click belly drum
- click liquidation/play rough
- win c:

Notes:
Surprise, another Belly Drummer. This one is a bit unique because of the unassuming numbers that rapidly become frightening. Huge Power doubles the attack of the user. Add the boost of the Rain and Mystic Water, and you have very big damage. You're only clicking Play Rough vs Dragon and Water teras, and Ice Punch vs Grass teras. Otherwise, just liquidate their assets. This is the original Belly Drummer, as it was used to literally One Shot 7-Star tera Dragon Charizards.

+6 252+ Atk Mystic Water Huge Power Azumarill Liquidation vs. 0 HP / 0 Def Gimmighoul in Rain: 1626-1914 (703.8 - 828.5%) -- guaranteed OHKO

Teammates:
Polotoed and Pelipper for Drizzle and Helping Hand. Want to see that number?
+6 252+ Atk Mystic Water Huge Power Azumarill Helping Hand Liquidation vs. 0 HP / 0 Def Gimmighoul in Rain: 2437-2868 (1054.9 - 1241.5%) -- guaranteed OHKO

There you go.

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Iron Hands - IRON CHEEKS (Tera Electric/Stellar) - Electric to boost Thunderpunch
- Click belly drum
- punch them w/ the super effective punch or drain punch if you're afraid of dying
- win c:

Notes:
Similar to Ursaluna, but notably it is weaker as the moves themselves do less damage (lower base power), and Quark Drive (when active) increases Iron Hands' attack by 30%. It's still absolutely silly with multipliers (electric terrain, punching glove, quark drive, STAB).
+6 252+ Atk Punching Glove Quark Drive Iron Hands Thunder Punch vs. 0 HP / 0 Def Gimmighoul in Electric Terrain: 1410-1659 (610.3 - 718.1%) -- guaranteed OHKO

Teammates:
Pincurchin works well. Alternatively, A Miraidon or anything that learns Electric Terrain (activates Quark Drive & increases the base power of Thunder Punch).

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Kingambit: Oda Nobunaga (Tera Dark/Stellar) - Dark to boost Kowtow Cleave
- Click Swords dance
- Kowtow CLEAVE anything not fighting/dark/fairy type
- Iron Head anything else
- Click assurance if you have a partner that you know will attack before you (they have a higher speed stat)
- win c:

Notes:
Not as immediately powerful as the last two, but a lot safer. Black Glasses + Tera Dark is pretty funny damage as well.

+2 252+ Atk Black Glasses Kingambit Kowtow Cleave vs. 0 HP / 0 Def Gimmighoul: 1008-1188 (436.3 - 514.2%) -- guaranteed OHKO
+2 252+ Atk Black Glasses Tera Dark Kingambit Kowtow Cleave vs. 0 HP / 0 Def Gimmighoul: 1344-1584 (581.8 - 685.7%) -- guaranteed OHKO

Teammates:
Tyranitar and Grimmsnarl are a good partner here, or anything that can learn Screech. Grimmsnarl can use Parting Shot on Kingambit, giving it +3 attack immediately due to defiant (Grimmsnarl cannot use Prankster though).

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Iron moth: The Literal Sun (Tera Fire/Poison) - Fire to boost Fiery Dance/Fire Blast, Poison to remove rock weakness
- Click Meteor Beam if the target isn't Steel/Fighting/Ground type
- Fiery Dance if you didn't meteor beam
- Keep dancing damn it
- Fire Blast if you're crazy, Sludge Wave if the target is Fairy type
- win c:

Notes:
Meteor Beam raises Iron Moth's special attack by 1 before attacking (meaning even if it misses, you still get the +1). Fiery Dance also can raise Special Attack by 1 50% of the time. It just kind of keeps getting stronger and stronger. Quark Drive will boost that special attack further by 30%, and Sun will boost the power of Fire Moves by 50%. Big damage.
+1 252+ SpA Quark Drive Iron Moth Fire Blast vs. 0 HP / 0 SpD Gimmighoul in Sun: 816-960 (353.2 - 415.5%) -- guaranteed OHKO

Teammates: Pincurchin works well, as do Torkoal and Ninetales (either one provides different utility, Sun from regular, Aurora Veil from Alola).

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Gouging Fire: this freak (Tera Fire/Dragon)- Fire to boost Heatcrash, Dragon to remove rock weakness
- Dance once or twice
- Heat Crash out
- Click dragon claw if target is dragon/water type
- Click earthquake if target is rock type
- Win c:

Notes:
Gouging Fire is exclusive to Scarlet fyi. Heat Crash does more damage the lighter the target is, and vs Gimmighoul it will always be at maximum power (120). Here's a sneak peek (with only 1 dragon dance in the sun).
+1 252+ Atk Charcoal Protosynthesis Gouging Fire Heat Crash (120 BP) vs. 0 HP / 0 Def Gimmighoul in Sun: 925-1090 (400.4 - 471.8%) -- guaranteed OHKO

Teammates:
Bring Torkoal or Ninetales for Drought. Additionally, Torkoal's helping Hand can boost the damage further by 50% (Ninetales can also use it).

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Walking Wake: Suicune but crazy (Tera Water/Stellar) - Water to boost Hydro Steam
- Snarl to activate throat spray
- STEAM anything not water/grass/dragon type
- Dragon Pulse the dragon/water types
- Flamethrower the grass types
- Win c:

Notes:
This essentially the special attacking version of Gouging Fire. Snarl will activate Throat Spray, giving Walking Wake +1 special attack. Hydro Steam is a unique water move that actually gets stronger in both Rain AND Sun by 50%. With Sun, you can activate Protosynthesis, so it's ideal. Mystic Water increases the power of Hydro Steam by 20%.

+1 252+ SpA Mystic Water Protosynthesis Tera Water Walking Wake Hydro Steam vs. 0 HP / 0 SpD Gimmighoul in Sun: 872-1028 (377.4 - 445%) -- guaranteed OHKO

Bring Torkoal or Ninetales for Drought. Additionally, Torkoal's helping Hand can boost the damage further by 50% (Ninetales can also use it), and Ninetales can use Fake Tears to destroy the special defense of the target. Rain setters can also help, but they're not giving the same damage numbers.

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Archaludon: The bridge (Tera Electric/Stellar) - Electric to boost Electroshot
- Click electroshot
- if the rain us up, keep clicking electroshot
- if it is not, click Flash Cannon or Dragon Pulse
- Click Body Press if you get hit a lot of times (Stamina raises your defense up each time you get hit)
- win c:

Notes:
When Rain is up, Electroshot does not need to charge. Meaning it's a 130 Base Power 100% accurate attack that also raises your Special Attack by 1 each time you use it. If it's not obvious, that's silly. Goofy, even. However, don't bring vs a Ground Tera, as it will be useless (you will still get the +1 though).
+3 252+ SpA Magnet Tera Electric Archaludon Electro Shot vs. 0 HP / 0 SpD Gimmighoul in Electric Terrain: 1183-1393 (512.1 - 603%) -- guaranteed OHKO
(Since the +1 goes off before the attack, the weakest Electroshot will still be at least +1).

Teammates:
Bring Pelipperor or Politoad for Drizzle. That way, you can use a Magnet instead of a Power Herb for 20% more damage on Electroshot. Pincurchin can also use Rain Dance AND provides electric terrain by default (but no helping hand). Funny!

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Armarouge: The rebel (Tera Psychic/Normal) - Psychic to boost Expanding Force, Normal to remove weakness to all attacks
- Calm Mind
- Get hit by Hex/Shadow Ball/Power Gem and activate the Weakness Policy
- Click Flamethrower or Expanding Force and blow that guy up
- win C:

Notes:
Armarouge is everything you don't want for the Gimmighoul tera raids, as it's weak to 3/4 of the attacking moves Gimmighoul will use. However, with Weakness Policy, that weakness becomes our advantage. Getting hit by a super effective attack will double Armarouge's attack and special attack (+2 to each), making Expanding Force and Flamethrower do massive damage. With the right support, this is a very easy attacker to use.

+2 252+ SpA Armarouge Expanding Force (120 BP) vs. 0 HP / 0 SpD Gimmighoul in Psychic Terrain: 729-858 (315.5 - 371.4%) -- guaranteed OHKO

Teammates:
Almost always should come with Indeedee, as it can helps support it the best. Grimmsnarl is a secondary option. The alternative is Torkoal or Ninetales if the enemy tera type is weak to fire (Grass/Ice/Steel/Bug).

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Supporters: None of these guys need to/should tera
Not listed in terms of effectiveness; each of these is ideal for different situations.
https://pokepast.es/1a399837ebb1cc6d

Politoed: The silly frog (Tera Water/Normal) - It's base typing is fine
Drizzle will activate as soon as you hit the field, boosting the power of water moves by 50%. Rain Dance should be used once the rain wears off/if it gets overwritten. Additionally, you can use Helping Hand to boost damage of your allies and mud-slap to reduce the enemy's accuracy.

Pelipper: the frigate (Tera Ground/Normal) - Remove the weakness to Rock
Similar to poli, except provides some more offensive utility with Hurricane (or can use Roost to heal). Keep in mind, Peli is better suited as a physical supporter, so it may not be ideal for these raids specifically. Note that you are weak to Power Gem.

Torkoal: sleepy turtle (Tera Ground/Normal) - Remove the weakness to Rock
Drought will activate as soon as you hit the field, activating Protosynthesis and increasing the power of Fire Moves (and Hydrosteam) by 50%. Sunny Day should be used once the sun wears off/if it gets overwritten. Helping Hand is there to provide damage buffs, and Yawn is there to put the enemy to bed (useful if working with Armarouge specifically, as it wants to take only 1 hit). Similar to Peli, Torkoal is much better suited as a physical supporter. Note that you are weak to Power Gem.

Ninetales: Fire Mia? (Tera Ground/Normal) - Remove the weakness to Rock
Similar to Torkoal, but with a lot of Special Defense instead of Physical defense. Additionally, with Fake Tears, you can trash Gimmighoul's special defense to help a special attacking partner like Iron Moth, Armarouge, or Walking Wake. Unfortunately, cannot learn Light Screen, so it is less useful for Armarouge specifically. Note that you are weak to Power Gem.

Pincurchin: Shayna's #1 Op (Tera Electric/Normal) - It's base typing is fine
Electric Surge activates Electric terrain as soon as you hit the field, activating Quark Drive and increasing the power of Electric Moves by 30%. Electric terrain should be used once the terrain wears off/if it gets overwritten. Unlike the other supports, Pincurchin does not have access to Helping Hand, but instead to Accupressure, which randomly raises any ally's stats by 2, making it ideal for Iron Moth and Archaludon. Archaludon especially given Pincurchin has access to Rain Dance, which will unlock Electroshot's full potential.

Indeedee: Ladies First! (Tera Stellar) - It's base typing is perfect
Psychic Surge activates Psychic terrain as soon as you hit the field, increasing the power of Psychic moves by 30% and doubling the power of Expanding Force. With access to Light Screen and Heal Pulse, this is the best Partner for Armarouge unless the target is tera Dark/Psychic (Armarouge shouldn't be going to these matchups in the first place). Note that the female is preferred here due to her higher defensive stats.

Ninetales-Alola: Ice Mia??? (Tera Ground/Normal) - Remove the weakness to Rock
Snow Warning will activate as soon as you hit the field. However, this is secondary, as the real reason to use Ninetales-Alola is for Aurora Veil, which acts as both Light Screen and Reflect at the same time. Additionally, like normal Ninetales, fake tears access makes it very useful for Armarouge due to Aurora Veil keeping it protected. Note that you are weak to Power Gem.

Tyranitar: Gettin' Dusty (Tera Stellar) - It's base typing is perfect
Sandstream will activate as soon as you hit the field, boosting the special defense of Rock types by 50% and damaging everything that isn't Ground/Rock/Steel type every turn. With Screech, you can trash Gimmighoul's physical defense, and with Rock Tomb you can lower its speed for your slower attacking allies to outspeed. Smack Down is there in theory to allow ground attacks to hit Tera Flying Gimmighoul, but it's kind of pointless (Ursaluna has Facade which does more anyway). Due to the Sand (yes, it's preferred over Unnerve), Ursaluna and Kingambit are the ideal partners. Neither care about weather, neither are hurt by Sand, and both benefit from the effects of Screech.

Grimmsnarl: Ugly Betty - (Tera Stellar) - It's base typing is perfect
With fantastic support options, you have a lot to work with. Light Screen to help anything weak to Rock or Ghost (Armarouge), Fake Tears to help any special attackers (Armarouge, Iron Moth, Walking Wake, Archaludon), Taunt to block the Gimmighoul's Nasty Plot, and Parting Shot to either boost a Defiant ally (Kingambit or Annihilape), or disrupt the enemy. Only real drawbacks are it does not provide weather/terrain, and if it's paired with Kingambit, it cannot use its best ability Prankster, and instead should use either of the other two.

Honorable Mentions:
Koraidon - has access to Screech and can set up the sun. Also, is not weak to Power Gem, unlike the other two Sun Setters.
Groudon - Can set up the sun and resists Power Gem.
Miraidon - Has access to Metal Sound, which acts the same as Fake Tears, and can set up Electric Terrain.
All three of these are either version exclusive or rare, and they're all so strong that they shouldn't be used as supports anyway.

Hippowdon - Has access to Sand but does not have access to Screech. Instead, has Yawn.