Joan Alter Site

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

She is best used in teams that can provide critical stars to maximize her high critical damage potential. Jeanne d'Arc Alter | TYPE-MOON Wiki | Fandom Joan Alter

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. comical "Santa" version exists

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.