In order of appearance/mention
Deltaspin
Ice-E's>Bunker
Ice-E(ID-IC)<>Gaster(Docster)
Vessel(A Robot Dude to Thrash Your Own Ass With)<>Thrash Machine(MACHINE)
Dess>Kris
Rudy>Asgore
Noelle>Asriel
Jevil(Jack)>Noelle
Temmie<>Jockington
Berdly(Aevyann Intelliejanc)<>Rouxls Kaard(Ramwell)
Seam(Sean)>Susie
Lancer<>Alvin(Clovyr)
Noelle's Original Ralsei Counterpart Version(Lorenel)>Ralsei
Top Chef<>Hacker
Old Man(Gearry)>Seam
C. Round(Cinisder)<>Mizzle(Mizzeant)
K. Round(Cinisder^2)<>Miss Mizzle(Mizzearch)
Ponman<>Cuptain
Susie(The Dragon)>Jevil
Sound of Justice(The Justice)>King
Pippins<>Itself(Chippins)
Jackenstien(Empourer)>Queen
Rudinn(Scrapguy)<>Plugboy(Pulgurr)
Sweet Cap'n Cakes(Swii, Nubert and Lukey)<> Mike Impersonators(Batto Ft. Plee and Jo)
Electro-Dasher(Danger Limo)<>Quiz Vortex(Teleportal)
Asriel(Azzure)>Addison
Relsay(Ralsreal)>Spamton
Unused Asriel Phase 2 Design From The Art Book>NEOTECH
Ralsei(Ralse)>Swatch
Kris(Kristovision)>Tenna
Shadowguy>Still Shadowguy(Cinemask)
Swatchling(Blocksling)>Zapper
Sword Route Generic Enemies(Agutsu and Tomereru)>Weather Duo
Ramb>No One(Scribb)
Watercooler<>Fireextinguisher
Zelda gameplay in Chapater 3<>PINO-8 Celeste
Sokobans>Climbing
ERAM(ADVERSARY)<>FRIEND(KRAD)
Swatch(Tober)>Dess
Angel(The Silenced Angel)Knight
King(Katoru Ito)>Old Man
Diner>Church
Cuptain(Checkmate)<>Ponman(Pepizen)
Clover(Scarly, Zure and Turq)>Jackenstien
Knight(Guardian)>Titan
Deltaswap: The One That Swaps Noelle With Dess
Kris(Chara)<>Asriel(Siler)
Noelle<>Dess
Devilsknife(Li'l Devvin)<>Lancer(Demonslance)
Jevil(The NEO CHAOS)<>King(Zealmon)
Spamton(NEOTE 
H)<>Queen(Bytebitt)
Small Mike(Cropho)<>Tenna(TV Anton)
Forgotten Man(ALLY)<>FRIEND(Lost Cat)
Cowboy Hat Mike<>The Tenna Statues From The TV World Dynamic Background That Were Leaked Before Chapter 3(Snail Anton)
Shadow Mantle (ERAM)<>DarkPlate(GRIORAN)
Titans<>Booms
Fetuspawns<>Koopa Shells
Deltaspin 2
Ramb(Ranbo the Clown)<>Jevil
ERAM>Seam
Monster Teen>Lancer
Starwalker and Starwalker Birds<>King(Chaintraveler and Chaintraveler Owls)
Knight(Mx. Nyte)>Queen