Alter - Joan

Here is a helpful summary of her character and usage in FGO:

Based on the search results, "Joan Alter" (often referred to as or Jalter ) is a popular character from the Fate/Grand Order (FGO) mobile game and anime franchise. She is a distorted, "Altered" version of the historical Joan of Arc, appearing as an Avenger-class servant designed to be a vengeful figure.

Born from a wish upon the Holy Grail by Gilles de Rais, she represents a twisted version of Jeanne d'Arc seeking revenge. Over time, she develops into her own person rather than just an imitation of her saintly self. Joan Alter

As an Avenger, she is a high-damage dealer, often noted for having some of the highest Attack (ATK) values in the game. Key Skills (Leveling Priority):

A party-wide damage boost that doubles for [Dragon] trait allies (level last). Here is a helpful summary of her character

A younger, comical "Santa" version exists, known as Santa Alter Lily.

Boosts critical damage (+50%) and star gathering rate for 3 turns (ideal to level first). Over time, she develops into her own person

Grants a 50% Buster buff for 1 turn (level second).