Eula is considered runner up to Ganyu. As an S tier 5 star, her play style and elemental burst/skill are amazing. Eula was added in the 1.5 update and almost imediately got attention. With the right build, Eula can ultimately destroy a hilichurl camp and specific bosses. She is a limited 5 star that you can only pull when her banner is up, but you won't regret waiting if you pull her.
Eula's skill is called "Glacial Illumination". When used Eula deals a great amount of cryo damage by creating a Lightfall Sword, this gives AoE damage. Eula's skill best used when attacking multiple people. Depending on the element of what you're attacking, she can probably instant kill it/one shot it.