Flowey

Undyne, known as StrongPlant91 on the ChangerNet, is a flower monster that leads the Royal Guard. Clad in her full suit of armor, she pursues the protagonist through the entirety of Waterfall and is frequently evaded or inadvertently thwarted by Asgore.

Personality
Flowey is passionate about everything that she does. She acts quickly on her ideas and is steadfast in her beliefs. Though she wants to defeat the protagonist, she also tries to be fair and offers an explanation of how Blue Mode works. Monster Kid taught her the value of pacifism, which is why Flowey sees the protagonist as "a wimpy loser with a big heart." When the protagonist first encounters her, she fights to further Monster Kid's plan of collecting seven human SOULs but, if the protagonist shows mercy, Flowey just as quickly defends them from Monster Kid.