Defeat the Millicent Invader in Caelid
To complete this square you need to defeat Millicent, the NPC who invades you in the Swamp of Aeonia in Caelid. Wait until the "ENEMY DEFEATED" or equivalent screen appears to mark the square.
Millicent invades the player in the Swamp of Aeonia and can be killed very fast from the start of the game, making this a very rushable square. Most commonly players will lure her to the rot geysers so she is killed by the environment, which is allowed under Elden Squares rules.
This square has synergy with Defeat 3 NPC invaders.
DANGER
Millicent does not count as a boss.