https://minecraft.fandom.com/wiki/Minecraft_Story_Mode:Cassie_Rose

Cassie Rose​ is a character in Minecraft: Story Mode and the hidden main antagonist in "​A Portal to Mystery". She has a pet cat named Winslow. She is voiced by Ashly Burch. She also has a persona, the serial murderer known only as of the White Pumpkin killer.

White Pumpkin Her persona, the White Pumpkin killer, is shown to lean more into Cassie Rose’s aggressive tendencies by being willing to kill her victims to claim an enchanted flint and steel. When the White Pumpkin is revealed to be Cassie Rose, she states that she was trapped in the YouTuber’s world for a very long time. Her time in their world likely caused her to be in her current mental state.