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"I couldn't tell him no about a sandwich," she said. "I couldn't tell him no about anything."
Mr Combs' legal team has not yet had the chance to question Mia, or respond to her claims.
She is the second witness in the New York trial to allege that Mr Combs sexually abused her, along with Mr Combs' ex-girlfriend, Casandra Ventura.
Mia testified that she started working for Mr Combs as a personal assistant in 2009 when she was in her mid-20s, joining what she described as a "chaotic" and "toxic" work environment.
"The highs were really high and the lows were really, really low," she told the court on Thursday.
The job required her being "always within eyesight" of Mr Combs, she testified, and "anticipating his needs, whims and moods".
She said she was often required to stay at his homes, where she could not lock the door or leave without the rapper's permission.
During her time working for Mr Combs, he was frequently violent towards her, Mia testified.
On one occasion, she said he threw a spaghetti bowl at her, which narrowly missed her head, Mia told the court.
Another time, she said Mr Combs forcefully threw his computer at Mia's head when she told him the wifi nearby was still being fixed, she testified.
She also testified about another situation when she witnessed Mr Combs being violent with his ex-girlfriend, Ms Ventura, who had became close friends with Mia during her time working for the rapper.
Mia once went on holiday with the couple in the Turks and Caicos, she told the court. One late night on the trip, she said Ms Ventura ran into her room screaming that Mr Combs was "going to kill me", she testified. They ran away and hid on the beach, she said.
Also on that holiday, Mia testified that she and Ms Ventura had used a paddle board to go into the water to escape Mr Combs, who was pacing back and forth on the beach. Before they knew it, the sky turned dark, portending a storm.
"I was trying to weigh if it was scarier to face mother nature, or go back to Puff [Mr Combs]," Mia testified.
Mia was also there one night in 2013 when she said that Mr Combs was banging on Ms Ventura's door in Los Angeles.
She testified that he attacked her and cut open her eyebrow when throwing her on to the bed frame. Mia told the court that she tried to jump on Mr Combs' back, but he threw her against the wall.
"He's actually going to kill her," Mia said she remembered thinking to herself.
Mia told the court that despite witnessing Mr Combs's abuse toward Ms Ventura, she did not report him because she "believed that Puff's authority was above the police".
She testified about multiple instances where she alleged Mr Combs sexually assaulted her, including one time when she said she woke up to him trying to rape her.