Mistilteinn Treesea

An evil dream demon who appears in the anime. She has the power to force dream demons into human vessels, later targeting and killing them, resulting in the vessel losing all ambition in their goals. She is extremely strong, as it is noted that she is acknowledged by Pharos Hercules for her power. However, thanks to Yumeji's confidence, she is killed by Merry and Engi. Source: Wikipedia