Illasera appears right at the beginning of plot of the expansion pack Baldur's Gate II: Throne of Bhaal. She challenges the player character after a prophecy spoken by the stone heads in the forest. If the player character is accompanied by their party from Baldur's Gate II: Shadows of Amn, she will have warriors helping her; if not, she will attack by herself. Regardless, as the first opponent in the expansion she is not very powerful and only uses relatively weak spells, even though she theoretically knows up to ninth-level ones. Her main mode of attack is by magic. As befits her nickname, she wears the Baldur's Gate version of Boots of Speed, increasing her movement speed but not her attack speed. She also wears a powerful elven chainmail.
Illasera is the only one of the Five who is not indicated as having a small army of her own, though the warriors accompanying her could well be part of one.
When Illasera tried to kill Abdel Adrian, she used arrows with runes carved on their sides that could pierce even his flesh and wound him. Abdel defeated her by turning into an avatar of Bhaal, starting to eat her after she had been crushed nearly to death in a tight and fatal "bear hug".