1.Substitute Doll.
https://cdn.bulbagarden.net/upload/a/a1/Substitute_artwork.png
I know this is a move but it move could be done like in anime:
https://cdn.bulbagarden.net/upload/b/b9/Togepi_Substitute.png
So this could be like Toy Pokemon ,similar to Banette just cute and not haunting. The name would be Gojon because it kinda reminds me of Godzilla, like tiny Godzilla. No evolution and it'd be introduced in Gen 2 because that Gen introduced many non evo Pokemon at the time. Also, I'd put it to change forms if it's day to be like Toy and Night to be small dragon( art similar to that tiny dragon seen as statues in the gyms).
So Day form: Normal. Night Form: Dragon. Not Leg/Mythical.
2.Void Shadows.
https://cdn.bulbagarden.net/upload/8/88/Void_Shadows.png
Now, these debut in Mystery Dungeon which is still a game territory despite not main games, still games. These little things could be Ghost type introduced in Gen 4. (Not Leg/Mythical). Also they could do something about Darkrai similar to Unown living in other dimension where Dialga/Palkia are. I'd call them Shadling. Shad= Shadow and ling like Chingling ( ling) which could be something like small or baby which they kinda look small and baby-like Ghost types.
3.Dark Rust.
https://cdn.bulbagarden.net/upload/0/09/Dark_Rust.png
4.Dark Matter
https://cdn.bulbagarden.net/upload/1/17/Dark_Matter.png
5.Bittercold
https://cdn.bulbagarden.net/upload/4/45/Bittercold_PMDGTI.png
Now I know these 3 things don't even look like Pokemon but some Pokemon don't like Pokemon either especially UB's and some Legs/Mythical. These things appeared in Rumble and MD which are still games. I think they should've been Pokemon. Now, I always thought of having like Virus Pokemon, I don't think we ever had one maybe Deoxys is(?) and that's about it. But these could be like Virus trio: one is making all technology go ape ****( Dark Rust , like computer virus), Bittercold makes Pokemon and Human have cold( like virus does) and Dark Matter IDK can maybe emit dark energy like virus to turn Pokemon and people "evil". So these 3 would be like Mythical trio. Dark Rust would be called: Rustent( I know bad name if someone can come out with better name for,I'd be glad), Psychic type( because of computer virus), Dark Matter: Negotent( same as Rustent; bad name, I came up with negative so Nego, I added tent lmao): Dark type. BIttercold:Glacitent ( Glaci because I am tired of Ice-freeze names, same as above if someone has better name fire it up), it's Ice type. I'd say these would be introduced in Gen 5 part of B2W2, IDK, I saw that gen 5 has a lot of Legs/Mythical so I went there.)
Ok now for remaining Pokemon I dug up Pokestar Studios opponent which are "fanmade" Pokemon yes but some of them could be treated as Leg/Mythical and UB's and they're "fanmade" Pokemon created by GameFreak itself, so they could've easily been actual Pokemon.
6.Brycen's Jet
https://peardian.tumblr.com/image/93371726278
I know this sounds super dumb but hear me out on this one. This Pokemon would've been introduced in Gen 5 in B2W2. I'd put that Team Plasma wanted to do similar thing to Kyruem which they have done in BW2 aka fusion. I'd put a story that they did some experiments with regular Pokemon, so they created thing thing, called Jetsorb( lol, Jet and sorb because it can absorb types)), like they took Togekiss, Tyranitar and Gengar and made it into one + some modifications. Seeing how it turned great they put some modifications on Kyurem so it could fuse with Z/R. This Jetsorb thing is Normal/Fire but can use ability which his Normal type changes to whatever type opponent has( except Fire because it can't be Fire/Fire). Example You send Emboar( Emboar is Fight, so Jetsorb is Fire/Fight, Samurott; Water/Fire, but if you choose dual type Pokemon that isn't fire like Noivern, Jetsorb gets a type that is Noivern's primal type which is IIRC Flying so Flying/Fire.(not Leg/Myth)
7. UFO.
https://cdn.bulbagarden.net/upload/c/c1/Spr_B2W2_UFO.png
Now ,there are some PS opponents that won't be here like Mecha Tyranitar, Monica, Black Belt etc. Even though this thing looks like Cascoon, still it's different and could be like Leg/Myth of Gen 6. It's like Alien Legendary Pokemon like Deoxys just in Gen 6. Now, tbh I don't know what he would do in games but I only thought about in anime. If someone watched XYZ, in the end you have that Megalith thing.
https://cdn.bulbagarden.net/upload/7/7f/Giant_Rock_2.png
I am now thinking that this UFO thing ,which I'd call him:Ivasol( because of Invading), since he's like alien invading the Earth, is replacing this the rock thing as in Lysandre wanted this Pokemon to be like Zygarde strength(like this Giant Rock) by giving him Mega energy Alain gathered because thing UFO thing has radiant energy inside already.( maybe in main games this UFO thing could be like reason for Mega or something). I'd put this Invasol to be Steel/Psychic(Legendary). SO basically, everything is same just think Invasol is that Giant Rock.
8.Old Statue
https://cdn.bulbagarden.net/upload/0/04/Spr_B2W2_Old_Statue.png
9.Majin
https://cdn.bulbagarden.net/upload/c/ca/Spr_5b2_Majin.png
10.F-00
https://cdn.bulbagarden.net/upload/4/4e/Spr_5b2_F-00.png
11.F-00(2)
https://cdn.bulbagarden.net/upload/6/68/Spr_5b2_F-00_2.png
12.Humanoid
https://cdn.bulbagarden.net/upload/5/5c/Spr_5b2_Humanoid.png
13. Monster
https://cdn.bulbagarden.net/upload/5/5b/Spr_B2W2_Monster.png
14. Black Door
https://cdn.bulbagarden.net/upload/9/98/Spr_5b2_Black_Door.png
15. Transport
https://cdn.bulbagarden.net/upload/1/1a/Spr_5b2_Transport.png
16. Alien
https://cdn.bulbagarden.net/upload/9/94/Spr_B2W2_Invader_Alien.png
So, all these things kinda look like UB's(except F-00,F002) they're weird so I decided to put them on Gen 7.Some in USUM, some in SM. This Old Statue thing: I call him Totemass( because of Totem + mass), I'd put him to be Water/Fairy UB Right side is water, left is Fairy and that ball would be like its life energy(also there's no Water and Fairy UBs). Majin ( the best looking non Pokemon, IMO) I'd call him Toxiboo( Toxic and Boo because it looks like Ghost), hence typing would be Ghost/Poison UB. F-00 and F-002. Now I'd call them artificial Pokemon like Magearna created by Lusamine and her stuff just like they created Silvally and Type Null. My story would be: they wanted to create a being who could battle UBs but they created this F-00 thing and he could evolve but it failed so they dumped it.And created Type Null( much more powerful + Legendary( F-00 is not Legendary)). So F-00 would be called Robbotix and is Steel type, and he evolves into F-002 who would be called Robobroke( because it's broken Robot again bad name) and is Dark/Steel type.
Humanoid and Monster look like Humanoid evolves into Monster so I put it to be like Poipole > Naganadel. Humanoid would be called: Ventripa( idk how I got that name, Ventripa probably from ventriloquist (Ventri I just added pa) and it'd be Normal UB( since UB's are lacking Normal types so I made it that way),it evolves into Monster which would be Ventrioctod( Same as Ventri + octod because that thing is like Octopus) and it'd be Ground/Psychic, also notice how Humanoid's legs go into a ground which would turn into this Octo monster. Lol. Black Door. I had called it : Walondor( idk why it just sounds cool). Type: Grass/Fire because that's what type it is in PS xd. Transport. Temport( port because it could transport people and Pokemon and tempore means time in Latin I think). Type would be :Electric/Ice( no Ice UB Pokemon and lack of Ice Pokemon in Alola) and finally Alien, which I call:Bealiette( idk, maybe because of Beauty), Type: Psychic. Also,maybe in story there would be 4 UB Titans: Walondor, Temport, Toxiboo and Totemass which Bealiette calls so you must go to each island and beat them together with guardians like Tapu Koko and you vs Toxiboo on Melemele.
As of forms; I found currently not counting SH/SW only 3 Pokemon that deserve more forms based on what it's been said around here: Castform, Wormadam and Rotom.
1.Castform has 3 forms: Sunny, Rainy and Snowy based on weather. But there are 4 more weathers. Clear Sky which I put it as Normal( aka original form), Sandstorm ( I put it as Rocky form as Ground type, there's Foggy areas; I put it as Foggy form and Ghost type, and finally there's Windy stuff or like Sky battles, where I put Castform as Flying type.
2.Wormadam has only 3 forms based on environment: Plant, Trash and Sandy: Plant is on Water/Grass stuff and it's Grass/Bug,Sandy is on rock/Ground areas so it's Ground/Bug, and Trash is in Cities,buildings, sewers etc , Steel/Bug. But there's more, I found 3 more environment which can be used and those are by moves like camouflage,Nature Gift/power because I couldn't articles about environment: so forms would've been: Snowy/Ice area: Bug/Ice, if it's Volcano area: Fire/Bug and if it's Burial Ground or Sky battles(Windy) Ghost/Bug. There's more like some grass/Water variants but those go under Plant/Sandy Cloak also there's Space and US but those don't count for Wormadam.
3.Rotom:He's Electric/Ghost. He can go to many household items and such: So 1.Heat Rotom( Fire/Electric)(oven), 2.Wash Rotom(Water/Electric)(washing machine), 3.Frost Rotom(Ice/Electric)(fridge),4.Fan Form(Flying/Electric) Fan, 5.Mow form( Grass/Electric) lawnmower, I am thinking about these:6. Toxic form( Poison/Electric) coffee maker ( like coffee inside turns purple like poison, 7.Computer form( Psychic/Electric) Laptop, 8.Sound form( Normal/Electric) Boombox, 9.Zap form (Bug/Electric) ZappBug Heater,10.Jack form( Rock/Ground) Jackhammer, 11.Blend form( Steel/Electric) Blender,12.Brawl(Fighting/Electric) arcade/slot machines, 13.Shade form( Dark/Electric) Lamp/Chandelure, 14.Candy form( Fairy/Electric) Candy maker.Dragon makes no sense and Rock is similar to Ground.