Deliberate mistake: Several of the matches Nacho loses, he should actually have won. In Mexican pro wrestling, it is illegal to rip another's mask off, and results in immediate disqualification. This happens twice to Nacho, both in the fight with the midgets and in the final against Ramses.
Continuity mistake: In the scene where Nacho is supposed to beat up the guys on his date with the nun, he's stretching by the wall. He sees two guys coming and jumps over to grab her. When he first grabs her, her left arm is free, but in the close up shot directly afterwards, her arms are both inside his.
Deliberate mistake: In the final fight, Nacho pins Ramses outside the ring. Under Lucha Libre rules, a pin must take place inside the ring to be valid, so Nacho would not have won a bout this way, and the announcer did not mention anything about there being any special rules or stipulations for the match, such as "Falls count anywhere".
Continuity mistake: In the scene where Nacho is singing at the pro wrestler party and Esqueleto is being pulled into the hole by the fat lady, you see the fat woman knock down the plant pot in one shot. In the next, it is standing again, and then after one more shot, it is fallen over again.