Andariel is a Demon and the boss from Act 1 in Diablo 2. She also returns in Diablo 4. She was first seem in the Rogue reveal trailer on 19 February 2021.
While we do not know how Andariel will have changed in Diablo 4, it's likely she will perform similar actions in Diablo 4.
Andariel is a poison-based creature, capable of spewing toxic green clouds as well as striking with her scorpion tail-like stingers. She has good foot speed and attacks relentlessly, but is vulnerable to fire and can't hurt characters with high poison resistance. Use poison resistance equipment and antidote potions when fighting Andariel.
Ancient Horadric texts record that Andariel and the other Lesser Evils once overthrew the three Prime Evils - Diablo, Mephisto and Baal - banishing them from Hell to our world. With this betrayal weighing against her, Andariel's presence in Sanctuary can only mean that the forces of Hell are once again aligned behind Diablo and his Brothers. While it is clear that the Maiden of Anguish is acting on behalf of Diablo to prevent anyone from following him eastward, it is also clear that she must be destroyed if the Lord of Terror is to be stopped.