In Tumbletale, roles are switched. Like Underswap, Storyshift, and Taletwist, characters such as Sans and Papyrus get other roles, such as Grillby and Muffet.
The first 'friend' you meet. Oh, wait. Your best 'fried', Flamey the Flame. Flamey is Grillby, but with Flowey's role. He's sarcastic and has Flowey's personality.
The Ruinsperson knocks away Flamey the Flame once he surrounds you with 'friendliness flames'. The Ruinsperson has the role of Toriel, and is the Riverperson, but switched the first part of their name. The Ruinsperson named the Ruins 'Ruinsplace'.
Asgore takes the role of Napstablook and is extremely timid and shy after being left by Toriel. You first meet him in the Ruinsplace.
You first meet Undyne in Snowdin Forest. Undyne introduces herself as "Undyne the Fish Lady." Undyne takes the role of Sans, and is determined to do the right thing, though she can be lazy when things don't matter to her. She is extremely protective of Alphys, who takes Papyrus's role, and knows a bit more than Alphys thinks. Undyne's left eye glows green in her Genocide battle.
The Genius Alphys! Alphys takes the role of Papyrus, and is Undyne's cleverest friend. Alphys is on a quest for knowledge, (she also wants to get in the royal guard) and is trained by Chara, head of the Royal Guard. Instead of spaghetti, Alphys makes chocolate ice cream (and sometimes seagrass flavor). She calls Undyne 'lazy gill' and has a long yellow scarf that can act as a cape.
Chara. The head of the royal guard. She is in the role of Undyne. She is extremely protective of Asriel and has a personal grudge against humans and her mother Toriel who left them behind to pursue her dream of becoming an Idol. Chara becomes 'Chara the Challenge' on the Genocide Route after you drain her HP to 0. Chara has the best stats in the game and her weapons of choice are serrated knives. Her themes include battle against a True Challenge (for the genocide run) and Chara (when you first meet her.) Also, Knives of Strategy (Neutral and Pacifist) and DIEEEEE (The theme that plays as she says her monologue). You can 'date' with Chara if you have no EXP. In the date, you make chocolate with Chara. Chara is extremely protective of Asriel.
The God Of Hyperdeath. Asriel Dreemurr. Asriel takes the role of Alphys. Dr. Asriel is extremely hard on himself, so he calls himself a "Hypergoner." He is aware of Chara's over protectiveness and is embarrassed that he relies on her to take care of him. You can 'date' with Asriel after you finish the game and do the Chara date.
Toriel. Toriel takes the role of Mettaton. Toriel is extremely protective of her children and turns into Toriel EX during the Neutral/Pacifist route and Toriel MOM during the Genocide route.