AllTheMons x Mega Showdown:

Adds 99% of the missing mons and some legendary (like Zarude, Lugia, Mewtwo or Rayquaza), as well as MSD item recipes (like Red/Adamant Orb) required for this addon. Also required for the Armored/Shadow Mewtwo models (for 2.0)

Eeveelutions Reimagined or CobbleMotion:

Both add animations to Sandy (Lana's Eevee) & their Eeveelutions. While Eeveelutions Reimagined only adds animations to the Eevee line - CobbleMotion includes animations for many other mons aswell! Use either CobbleMotion or Eeveelutions Reimagined, using both could lead to issues!

OJ's Animations:

Adds animations to Zarude (sadly this addon has since been removed from modrinth)

Pledge Fragment:

Gives Keldeo its resolute form appearance when held in its cosmetic slot

Water Shuriken:

Gives Greninja its Ash Greninja appearance when held in its cosmetic slot

Radiating Zygarde Core (planned):

Gives any Zygarde its 100% form appearance when held in its cosmetic slot

Magic Music Sheet (planned):

Gives Meloetta its Pirouette form appearance when held in its cosmetic slot

How does the Shadow Type work?

General info:

• The Shadow-type has its own Tera, Z-Crystal, moves, type-effectiveness and much more
• Currently the only two Shadow Pokémon are Mewtwo & Lugia

Shadow Energy:

• To turn Pokémon into their Shadow variants you need a Shadow Energy
• Using it requires 250+ friendship with Lugia/Mewtwo and resets its friendship to 0
  

Type Chart & effectiveness:

• Shadow moves are 2x effective against every type (2x against dual types as well)
• Shadow moves are 0.5x effective against shadow itself
• Shadow Pokémon take neutral damage from all types (except Shadow) and have no immunities

Shadow Pokémon:

• Shadow Pokémon lose their original type and turn into pure Shadow-type
• Shadow Pokémon keep their original type STAB (as well as getting Shadow STAB)

Shadow Moves:

Black Vortex

• Shadow type's signature Z-Move (requires Shadowium-Z)
• Damage calculates based on the move used as a base

Max Void

• Shadow type's signature Dynamax Move
• Damage calculates based on the move used as a base
• Boosts speed of the user & allies

Shadow Blast:

• Shadow version of Aeroblast
• 80 bp, 100% accuracy, 5 pp, physical
• Has an increased critical hit ratio

Shadow Down:

• Shadow version of Screech
• 100% accuracy, 10 pp, status
• Lowers the Defense of all opponents by two stages each

Shadow Shed:

• 100% accuracy, 5 pp, status
• Removes effects of Safeguard, Reflect, & Light Screen from the opponent's field

Shadow Storm:

• 95 bp, 100% accuracy, 5 pp, physical
• Hits all opponents

Stats, Abilities and any other info:

Shadow Lugia

Stats: Same as regular Lugia
Ability: Shadow Pressure and Shadow Guard (same abilities as regular Lugia, just different names)
Moves: Regular Lugia move pool + Shadow Blast, Shadow Shed, Shadow Down & Shadow Storm (check the Shadow-type section for more info on those)

Shadow Mewtwo

Stats: +20% Atk/SpA & -20% Def/Spd
Ability: Shadow Boost (boosts super effective moves by 1.25x)
Moves: Regular Mewtwo move pool + Shadow Blast, Shadow Shed, Shadow Down & Shadow Storm (check the Shadow-type section for more info on those)

How do I get them?

Requires ATM x MSD to obtain Lugia/Mewtwo as well as to have/see the Shadow Mewtwo model (for Lost Lore v2.0 only)
Use the Shadow Energy on Lugia/Mewtwo to turn them into their Shadow Forms
Requires at least 250 friendship to use it & resets it back to 0
Can be reversed by using it again

Stats, Abilities and any other info:

Stats: HP: 106, ATK: 130, DEF: 110, SP ATK: 90, SP DEF: 154, SPD: 90
Ability: Battle Armor (prevents the opponent from landing a critical hit)
Moves: Regular Mewtwo move pool + Metal Claw, Iron Defense, Iron Head, Bullet Punch, Screech, Smart Strike, Flash Cannon, Iron Tail, Meteor Mash, Sunsteel Strike
Notes: Mega Evolves into regular Mega X/Y - tho I plan on giving it a custom mega!

How do I get it?

Requires ATM x MSD to obtain Mewtwo as well as to have/see the model (for Lost Lore v2.0 only)
Use the Binding Armor on Mewtwo to turn it into Armored Mewtwo
Can be reversed by using it again

Stats, Abilities and any other info:

Fully Cosmetic Forms so nothing of interest here!
Costumes include the Mystery Dungeon Scarfs, as well as the Costume Party, Martial Arts, Concert, Space, Captain, Cafe, Chef, Ruins and Holiday Costumes from Unite

How do I get them?

Give Riolu/Lucario a green/red scarf to hold (cosmetic slot) to turn them into the PMD/PSMD forms
Use the Costume Box on Lucario to switch between its many outfits from Unite
Can be reversed by unequiping the scarfs or circling through all costumes

Stats, Abilities and any other info:

Fully Cosmetic Forms so nothing of interest here!
Costumes include the Astronaut, Champion, Band, Bionicle, Cafe, Dancer Shorts, Detective, El Brave, Pride Shirt (+ Ace, Bi, Pan & Trans Pride variants), Rivals of Aether, Royal Mask, Santa, Summer, Team Magma (+ OR/AS variant), Team Rocket (+ Anime variant), Team Skull & Tekken costumes

How do I get them?

Use the Costume Box on Incineroar to switch between its many outfits
Can be reversed by circling through all costumes once

Stats, Abilities and any other info:

Fully Cosmetic Form so nothing of interest here!

How do I get it?

Give Pichu an ancient light ball to hold (cosmetic slot) to turn it Spiky-Eared
Can be reversed by unequiping it

Stats, Abilities and any other info:

Stats: HP: 113, ATK: 97, DEF: 130, SP ATK: 147, SP DEF: 113, SPD: 70
Typing: Ground & Poison
Abilities: Thermal Exchange & Earth Eater
Moves: Losely based on Groudons move pool, features many fitting grass, ground & poison moves

How do I get it?

Requires ATM x MSD to obtain Groudon and the recipe for the needed red orb
Use the Corrupted wish on Groudon to turn it into Meta/Virus Groudon
Can be reversed by using it again

Stats, Abilities and any other info:

Stats: HP: 100, ATK: 140, DEF: 140, SP ATK: 180, SP DEF: 110, SPD: 110
Ability: Full Metal Body (Stats can’t be lowered by opponent)

How do I get it?

Requires ATM x MSD to obtain Dialga and the recipe for the needed adamant orb
Give Dialga a Time Gear to hold to turn it into Primal Dialga
Can be reversed by unequiping

Stats, Abilities and any other info:

Fully Cosmetic Form so nothing of interest here!

How do I get it?

Requires ATM x MSD to obtain Zarude naturally
Give Zarude a ripped cape to hold (cosmetic slot) to turn it into Dada
Can be reversed by unequiping it

Stats, Abilities and any other info:

Shopkeeper

Basically a regular Kecleon with unique colors
The Shopkeeper is always male (it's the Kecleon Brothers afterall)

Reddy

Significantly harder to catch than regular Kecleons
Reddy is always male

How do I get them?

Both spawn in the same locations as regular Kecleons
The Shopkeeper always spawns with its brother - a regular Kecleon
Reddy is a rare spawn

Stats, Abilities and any other info:

MT:

Stats: 600 BST (100 in each stat)
Typing: Mono Steel type
Ability: Analytic

MT2:

Stats: 600 BST (100 in each stat)
Typing: Steel & Electric type
Ability: Flash Fire

How do I get them?

Ultra Rare spawns anywhere in the overworld (not near villages)
MT spawns at level 63 with its event moves and 3+ perfect IVs
MT2 spawns at level 72 with its event moves and 5+ perfect IVs

Stats, Abilities and any other info:

Snowman Munchlax

Typing: Normal & Ice Type
Abilities: Ice Body, Thick Fat, Hustle (hidden)
Moves: Same as regular Munchlax + lots of ice moves
Evolution: Evolves normally into Snowman Snorlax

Snowman Snorlax

Typing: Normal & Ice Type
Abilities: Ice Body, Thick Fat, Fur Coat (hidden)
Moves: Same as regular Snorlax + lots of ice moves
Notes: Can use its Z-Move, Gmax and Gmax-Replenish normally

How do I get them?

Rare spawn in snowy biomes

Stats, Abilities and any other info:

Illusionary Rayquaza

Typing: Ghost/Flying type
Stats: Same as Rayquaza, SpD & Spe raised to 105 to match Mismagius'
Moves: A combination of both Mismagius' & Rayquazas move pools

Illusionary Mega Rayquaza

Typing: Dragon/Flying type (due to coding limitations on my end)
Stats: Same as Mega Rayquaza

How do I get it?

Requires ATM x MSD to obtain Rayquaza naturally
Use Dream Catcher on a Mismagius and afterwards on a Rayquaza
Can be reversed by using the item again

Stats, Abilities and any other info:

All Eeveelutions of Sandy have their own unique Hairstyles
Evolution: Evolves normally into all eevee evolutions
Notes: Can use its Z-Move, Gmax and Gmax-Cuddle normally

How do I get them?

Rare spawn in Woodland Mansions
Give Eevee or any Eeveelution shears to hold (cosmetic slot) to turn it into Sandy
Can be reversed by unequiping it

Stats, Abilities and any other info:

Mimikins is always female and its shiny is inverted
Notes: Can use its Z-Crystal & Ability normally

How do I get it?

Ultra-Rare spawn in the Deep Dark

Stats, Abilities and any other info:

Stats: HP: 105, ATK: 164, DEF: 130, SP ATK: 50, SP DEF: 130, SPD: 101
Moves: Expanded its move pool to closer reflect his appearance in the manga
Notes: Cannot Mega evolve, breed, or be evolved into

Custom Z Move/Crystal:

Dark Tyranitarium-Z transforms the move Rock Wrecker into Kaiju Cataclysm
Hits all Pokémon on the field, removes terrain, raises both its defenses & makes all targets flinch

How do I get it?

Ultra rare spawn at level 100 in naturally generated villages (Vanilla & BCA)

Stats, Abilities and any other info:

Evolution: Evolves into Crystal Steelix normally (trade + metal coat)
Ability: Entire line has the ability Water Absorb
Notes: Mega evolves normally

How do I get it?

Onix is a rare spawn in caves/underground, Steelix has to be evolved into

Stats, Abilities and any other info:

Levelling: They require less EXP to level up (fast experience group)
Notes: They can mega evolve normally

How do I get them?

Put a Nether Star and a Charcoal Stick/Miracle Seed/Mystic Water into a Resurrection Machine
They come with 4+ random perfect IVs