Mimi was a boss from Super Paper Mario. She was a boss in Chapter 2 and in Chapter 8. She was a mini-boss in Chapter 6. Mimi has powers of deception and can become invincible under Bleck's powers.
Mimi posed as a maid and tricked Mario by going into death traps. She failed and was chased out by a dog like creature. In 2-3, Mario repayed her 1 million rubies. In 2-4, Mimi chased Mario down the mansion basement and fought her. Mimi was defeated and retreated.
In Chapter 6, she served as mini boss to distract Mario as he attempted to get the pure heart from the crumbling dimension. She succeeded and the dimension was destroyed.
In 8-2, Peach faced off with Mimi. As they fought, Peach ended up winning. A trap floor opened and Mario and Luigi move on as they hear a giant crumble. Mimi also gave power to Mario in 8-4 to defeat Super Dimentio.
After the destruction of the void, she reformed to good in Flipside.