In his report, Mueller wrote that Mifsud had "connections to Russia" and former FBI officials have described him as a Russian agent.
In court papers, prosecutors denied withholding evidence and scoffed at the conspiracy theories promoted by Powell and her team.
"Since the beginning of their involvement, the defendant's new counsel have sought to get the charges dropped, professed their client's actual innocence, and perpetuated conspiracy theories, all while stating that the defendant does not intend to withdraw his guilty plea," federal prosecutors wrote.
Flynn's efforts to get more evidence, prosecutors argued, is "a fishing expedition in hopes of advancing conspiracy theories related to the U.S. government's investigation into Russian interference in the 2016 presidential election."
A Justice Department spokeswoman and Powell declined to comment. Sullivan has not indicated when he might rule on the defense team's motions.
If the judge sides with prosecutors, Flynn could be in trouble, legal experts said.
"If the judge disagrees with Flynn's arguments and concludes that Flynn is not fully accepting responsibility for his misconduct, then I would expect Judge Sullivan to say as much at sentencing and give a sentence that takes that lack of acceptance into account," said Steven Levin, a former federal prosecutor.
Levin and other legal experts say that by not withdrawing his guilty plea, Flynn has kept prosecutors from charging him with more serious crimes.
As part of his plea, for example, Flynn admitted he made false statements about consulting work he did for Turkey. If he were charged with more serious offenses and lost at trial, he could face extended prison time.
Prosecutors also do not appear eager for the plea to evaporate, the experts said. A trial would take time and they have problematic witnesses, including the FBI agents who had an affair and sent anti-Trump text messages.