Flowey Dreemurr

"Frisk! Is that really you, or is the sunlight playing tricks on me?"

-Flowey to Frisk, The Great Unknown.

Flowey is a male talking flower from the Undertale universe. He lives in the Underground with Asgore, Toriel, Asriel, and Frisk.

Appearance
Flowey is a talking flower with a white face and six plump yellow petals. He stands on a light green stem with two leaves of the same color and has beady black eyes and a mouth with two incisors.

Personality
In the original Undertale, Flowey has a cruel and psychopathic reputation and tries to kill Frisk when she first arrives in the Underground. However, in the World of Fantasia series, this is false. Instead, he is kind and quiet but can be sassy and sharp-mouthed at times, much like his Underfell counterpart. He is said to have helped Frisk through the Underground (again, similar to Underfell).

Between Books/Before the Girls
When Asriel died, his dust was scattered across his father's garden. A small golden flower sprouted from the ground right before Toriel left. After the third human--Alina, the Soul of Integrity--died, Asgore asked the Royal Scientist before Alphys, Dr. Gaster, to find another way to break the Barrier. Gaster then started his projects with Determination and decided to use the first golden flower in Asgore's garden as a primary test subject. He injected Determination into the flower, and after a few days, it disappeared.

Asriel then woke up in his father's garden, trapped in the form of a flower. Asgore soon found him, but couldn't put his finger on how the flower was familiar to him. Asriel ran away to the Ruins to in search of his mother, Toriel. He found her, but she didn't remember him either. Asriel then discovered his ability to Reset but doesn't, now going by "Flowey". When he met River (more commonly known as the River Person), the Caprian monster had a troubling vision of Flowey's future if he chooses to kill. He makes Flowey promise not to kill anyone or anything for as long as he lives, and Flowey agrees.

Twenty years after the sixth human fell, Frisk fell into the Underground and befriended Flowey. He resisted the urge to kill her and assisted her throughout the Underground. He then discovered that (unknown to Frisk) she was the reincarnation of his sister, Chara. Flowey didn't tell Frisk until she reached New Home and discovered that she and Flowey were family. After making friends with Asgore and facing Asriel, Flowey was accepted into the Dreemurr family as the Prince of the Underground.

Chapter 10: The Ruins
Flowey first appears at the start of the Ruins and meets Alex and Cassie. He goes through the Ruins with Frisk and the girls all the way to Toriel's old house. The next day, he, Frisk and the girls leave the Ruins for Snowdin.

Chapter 11: Snowdin
Flowey is quiet most of the time while he, Frisk, the girls, Sans, and Papyrus are traveling through Snowdin. The only time he speaks is when he corrects Papyrus for pronouncing his name.

Chapter 12: Waterfall
Flowey is mostly quiet while he, Frisk, the girls, and the skelebros journey through Waterfall to Undyne's house, and only speaks when he asks the girls what Gerson said about their amulets, when he tells the girls about his disliking for Temmies, and when he tells the group that they're almost to Hotland.

Trivia

 * Much of Flowey's kind personality is based off of that of Underfell.
 * Flowey and Asriel are twin brothers.
 * When monsters die, their Souls shatter and their bodies turn to dust. At the deceased monster's funeral, the monsters present take the dead monster's dust and spread it on the monster's favorite thing. Then, the deceased monster's essence lives on that object forever. When Asriel died, his dust was spread across his father's garden and a golden flower bloomed from the place he died right before Toriel left New Home. Flowey has a small piece of Asriel's Soul inside of his own, thus making them twin brothers.
 * Flowey is the reincarnation of Asriel.