Ruby hack: Ridiculous Ruby

Note: there will be some enemy-trainer-exclusive Pokemon added but you won't have to worry about them until very late in the game. The Pokemon below are roughly ordered by type of the Pokemon being removed.

Hoothoot line - Rufflet line
Pidgey line - Starly line
Sentret line - Glameow line
Jigglypuff line - Lillipup line
Ditto - Ambipom
Lickitung - Magnezone
Snubbull line and Mr. Mime - Goomy line

Weedle line - Venipede line
Surskit line - Dwebble line
Venonat line - Skorupi line
Shuckle - Durant
Ledyba line - Pancham line
Spinarak line - Phantump line

Absol - Spiritomb
Sneasel - Honchkrow

Plusle and Minun - Joltik line
Mareep line - Shinx line

Meditite line - Riolu line
Hitmonchan/lee/top and Tyrogue - Mienfoo and Scraggy lines

Slugma line - Frillish line
Torkoal - Heatmor
Vulpix line - Pansear line

Togepi line - Drifloon line
Yanma - Sigilyph

Shuppet line - Golett line
Misdreavus - Dusknoir

Hoppip line - Sewaddle line
Paras line - Pansage line
Tangela - Carnivine
Chikorita line - Turtwig line
Roselia - Cryogonal
Sunkern line - Electivire and Magmortar

Gligar and Delibird - Hippopotas line
Swinub line - Drilbur line

Snorunt line - Cubchoo line

Spoink line - Elgyem line

Sudowoodo - Rhyperior

Nosepass, Omanyte, and Omastar - Garchomp line
Kabuto and Kabutops - Panpour line

There aren't many changes to BSTs, and these are mostly just to balance out Pokemon that are hurt by the lack of a physical/special split.
Shinx, Luxio, and Luxray all have -10 in Attack and +10 to Special Attack.

Scraggy now has -5 in Defense and Special Defense but +10 in Special Attack
Scrafty now has -15 in Defense and Special Defense but +35 in Special Attack

Pangoro now has +5 to Special Attack

Trevenant now has +10 to Special Attack

There aren't many changes to types either.
Luxray is now Electric/Dark

Beartic is now Ice/Fighting

Pichu to Pikachu at level 15
Cleffa to Clefairy at level 15

Kadabra to Alakazam at level 36
Graveler to Golem at level 38
Haunter to Gengar at level 40
Machoke to Machamp at level 42

Onix to Steelix at level 34

Poliwhirl to Politoed with Sun Stone

Slowpoke to Slowking with Sun Stone

Seadra to Kingdra at level 48

Scyther to Scizor at level 37

Porygon to Porygon2 at level 30

Feebas to Milotic at level 20

Clamperl to Huntail at level 20 (high personality)
Clamperl to Gorebyss at level 20 (low personality)

Eevee to Espeon with Sun Stone
Eevee to Umbreon with Moon Stone

Magneton to Magnezone at level 45
Glameow to Purugly at level 30
Aipom to Ambipom at level 32
Murkrow to Honchkrow with Moon Stone
Dusclops to Dusknoir with Moon Stone
Rhydon to Rhyperior at level 52
Electabuzz to Electivire at level 46
Magmar to Magmortar at level 46

Mienfoo to Mienshao at level 44
Rufflet to Braviary at level 34

Pancham to Pangoro at level 32
Phantump to Trevenant at level 42
Goomy to Sliggoo at level 30
Sliggoo to Goodra at level 50

Furthermore, all Pokemon that evolve via stone will learn moves at the same (or a similar) pace to its pre-evolved form, so there's no real penalty for using an evolutionary stone early. Like, some Pokemon won't learn all the moves that their pre-evolved forms can, but they might still learn the important/good moves at a similar pace. In almost all cases, it's best to evolve Pokemon as soon as possible.

Gifts:
A familiar face in Fallarbor will offer you one of my favorite Pokemon lines
The Pokemon Egg in Lavaridge now hatches into a Pokemon that can do many more things than Wynaut ever could
At the weather institute, you get a new Pokemon that has an affinity with weather
The fossil Pokemon you choose will come at a higher level

Trades:
The kid in Rustboro will still want a Slakoth, but you'll get a very different Fighting-Type Pokemon in return
The basketball fan in Fortree will ask for a Pokemon related to the Miami heat and will give you his MVP rival in return
The lady in Pacifidlog will offer one of the most powerful Pokemon in exchange for one of the most common Pokemon

Interactable Pokemon:
So far, I've only added 1 interactable Pokemon on Route 119. I'm not sure if there will be more added.

Here are the Gym Leaders, their types, TMs, and the level of their ace Pokemon.

Damien, Dark, Thief - 17
Brooke, Water, Water Pulse - 20
Ivy, Poison, Toxic - 27
Robin, Flying, Aerial Ace - 33
Steele, Steel, Iron Tail - 35
Antonio, Bug, Flamethrower - 42
Terrance, Ground, Earthquake - 50
Buffy, Ghost, Shadow Ball - 55

Elite Four
Fighting - 57
Water - 58
Dragon - 59
Steel/Psychic - 60
??? - 62

- No Physical/Special split. Sorry.
- Once Surf is obtained, the intended order of progression is Route 105 through 109 (plus Route 115, New Mauville, and Abandoned Ship) -> Route 118 through 123 (including Weather Institute) -> Fortree Gym -> Mt. Pyre -> Lilycove Rival and Magma Hideout. I know this may not be the progression that most people do, but this is what I usually did.
- Name for the hack is not 100% certain, so don't be too surprised if I change it.
- Some moves have been edited to their power/accuracy in future generations. However, I'm stupid and forgot to record them so I don't know all of them. I know Outrage, Leaf Blade, and Giga Drain were edited. I don't know if that's all I changed or if I changed more. Sorry.
- There are some Pokemon whose RSE sprites I think are just awful in comparison to their FRLG sprites. They have been updated with their FRLG counterparts.
- There will be a few added NPCs who will sell TMs. As of right now, the only one is found in the Abandoned Ship and he just sells the original Gym Leader TMs that were not replaced in the game. Furthermore, evolutionary stones are purchasable in a new area and I will add someone who sells Heart Scales right before the Elite Four.
- Many new Pokemon get notable egg/tutor moves via Heart Scale now.

- Dex entries are unedited and will most likely remain that way. That does mean that Low Kick damage might not be exactly what it should be for some Pokemon, but that shouldn't be a big issue.
- I am a lazy hacker so while Norman and his sprite are being replaced, the text between he and Wally is still there at the beginning of the game. Just ignore it. The new leader's name is Steele and he's not supposed to be your father.
- Egg groups haven't been edited, so if you want to breed babies it's gonna be really ♥♥♥♥ed up. Also, Ambipom is in Ditto's slot now so it should serve the same function in breeding.
- Because Gen 6 Pokemon were added later, it is possible that some wild Pokemon and Trainers' Pokemon were altered because of it. So if you see any Gen 6 Pokemon before Gym 5 or so, please let me know. For example, if a Bug Catcher has Phantump or Pangoro or something like that please report it to me.
- Trick House is completely unedited.

Wiznatts, Chaos Rush, PsychoToxin, and anyone else who made 64x64 Pokemon and trainer sprites
Advance Series
UNLZ
A-Starter
A-Map
Move Editor
Trader Advanced
NSE
XSE
YAPE

Fighting - 57
Water - 58
Dragon - 59
Steel/Psychic - 60
??? - 62