Where the art comes from, and who drew it.
Pokemon artwork comes straight from the official games via PokeAPI.
The animated battle sprites are Black/White-styled sprites from the Smogon Sprite Project, which draws them for Generation 6 onward in the style of the Generation 5 games.
Some of the animations the project has not covered yet come from Ghasty001's animated sprite collection, shared free to use with credit. Credit goes to Ghasty001 for the animation work and to the spriters whose base sprites it builds on: Anarlaurendil, Antiant, arionelle, AshnixsLaw, aXl, Bloxable, Falgaia, hellfire0raptor, hexagonereal, Katten, KingOfThe-X-Roads, kiriaura, Kyledove, lennybitao, leParagon, mangalos810, Sleet and uppa.
The Pokemon walking around in The Deep are sprite sheets from SpriteCollab, the Pokemon Mystery Dungeon sprite project run by PMDCollab, used unmodified across 808 species. They are licensed CC BY-NC 4.0, copyright their contributors, and offered as-is with no warranty of any kind. Credit goes to all 67 of them: ◥θ┴θ◤, 3P1C, anomalocaris, Anon, Audino, avalancheman, Axcel, baronessfaron, bwappi, Caitemis, CHUNSOFT, cyboy_bit, DavKriz, Deeshura, DeltaL, dmDash, Emboarger, Emmuffin, FlowerSnek, FrivolousAqua, G〜, Ginnie, Grimlin, Hanbei, Ichor, Inv3rse, JFain, Jhony-Rex, Johanne2, JustAGunk, Katach314, Kawaiitron, KCN015, LazerBlitz, Leif, LightBlueBlaze, Limomon, Michael12, Mitsubachi, mixy:3, mosscoated, nataniel-sama, Neat_Neato, NeroIntruder, NickOnimura, NikolaP, Noivern, Noo, pi3.14, Pink_no_tori, Pokejavi., powercristal, Reimu\_needs\_$$$, RelicCipher, Riodise, Sceptile, Shadowcrafts, ShyStarryRain, Smalusion, Soulja, Spikey-Valentine, stressparticles, Tainted#3886, TawnySoup, Top_Kec, Uni, VOID.
Some of those sheets are official Chunsoft art rather than fan work, which is why CHUNSOFT is in that list.
NonCommercial is the one condition credit cannot buy its way out of, and it is the reason this art can live here: Rinne is an unofficial fan project that takes no money. Those sheets cannot travel to a commercial work, whatever else is stripped out of it first.
The full licence notice, including the disclaimer of warranties and the per-species credit, is kept beside the art in assets/exploration/sprite/CREDITS.md.
Trainer sprites in Season 2 are pixel sprites from the official games, drawn over a colored band behind each trainer.
FireRed and LeafGreen trainers (Lorelei, Agatha, Blaine in battle, the route trainers on the roads, every challenger at Cerulean Cave after the story, and some grunts), the close-ups of Giovanni and Petrel and the battle floors come from the Pokemon Essentials asset pack, credited to Luka S.J., Maruno, Marin, Pokecheck.org, PinkCatDragon, Tebited15, BadSamaritan, WolfPP, redblueyellow, Damien, Issei Hyoudou, Nasasu, luckygirl88 and Manurocker95.
Armoured Mewtwo's battle sprite is by Othienka, used with credit.
The Kanto badges are FireRed and LeafGreen's own, from the pret/pokefirered disassembly, recolored for Rinne.
The Liberator ribbon and the Season 1 ribbons are from Pokemon Sword and Shield, ripped by Random Talking Bush for The Spriters Resource.
The Season 2 backgrounds, Gym art, story scenes and Blaine's portrait in dialogue were made for Rinne.
Trainer sprites, battle floors and item icons across the game come from the Pokemon Essentials asset pack, credited to Luka S.J., Maruno, Marin, Pokecheck.org, PinkCatDragon, Tebited15, BadSamaritan, WolfPP, redblueyellow, Damien, Issei Hyoudou, Nasasu, luckygirl88 and Manurocker95.
The ribbons are from Pokemon Sword and Shield, ripped by Random Talking Bush for The Spriters Resource.
The Deep's tilesets are from Pokemon Mystery Dungeon: Red Rescue Team and Explorers of Time and Darkness, through The Spriters Resource. Tiny Woods and Beach Cave were ripped and formatted by SilverDeoxys563; Lush Prairie, Tiny Meadow, Apple Woods, Murky Cave, Mt. Bristle and Dark Hill are credited on their asset pages; the items sheet is by NULL, ripped by redblueyellow.
The site cursor is from Cookie Clicker Cursors by Galactic Nerds. The Arcanine and Mew cursors are Arcanine (Updated) and Mew Battle Mode from The Mew Collection, and the Halloween Darkrai cursor is Darkrai (cursor 14492). All four are from rw-designer.com, released to the public domain.
Pokemon, all Pokemon character names, and their sprites and artwork are trademarks and copyrights of Nintendo, Game Freak, Creatures Inc., and The Pokemon Company. This is an unofficial, non-commercial fan project not affiliated with or endorsed by any of them.