Andres Manuel Lopez Obrador, who narrowly lost Mexico's presidential election, has used his own TV programme to attack his rival's policies.
Mr Lopez Obrador lost last year's run-off by half a percentage point
In the first edition of his late-night TV programme he mocked the government's battle against crime and unemployment.
"The Truth Will Be Told", paid for by Mr Lopez Obrador's supporters, also featured a spoof news broadcast.
Mr Lopez Obrador has never accepted his defeat in Mexico's presidential run-off against Felipe Calderon in July 2006.
He proclaimed himself "legitimate president" after losing by less than one percentage point, calling for street protests that paralysed Mexico City for weeks.
The left-leaning Mr Lopez Obrador says that launching his own television show is the only way to ensure his policies are heard.
"This year, unfortunately, is looking really bad," he said during the programme, which was broadcast early on Tuesday morning.
"We had already predicted it. We had already warned of it, that things were not going to change with the right."
He said members of his left-leaning Democratic Revolution Party were in the process of submitting a bill to congress to lower prices by breaking up Mexican monopolies.
Mr Lopez Obrador and his supporters say the mainstream Mexican media has ignored him and the left-wing movement he represents.
The BBC's Duncan Kennedy, in Mexico City, says that although its middle-of-the-night time slot might not be a ratings winner, Mr Lopez Obrador believes it is the only way his agenda of helping the nation's poor will stand any chance of exposure.