Who the hell from nafta uses pesos in Mexico?

Nah.. I don't know, I guess if you've read the bank's webpage, that helps a lot. Just remember that the 20 & 50 bills are the same size, and they are the plastic kind like the Australian/NZ currency. You'll sometimes run into older paper 20s and 50s.

The 100, 200, and 500 bills are also the same size, but larger than the 20 & 50, and they are still paper bills, strangely enough. Anything dated before 1993 is invalid. Anything that says "Nuevo Peso" 1993 or later is technically legal, but no shopkeeper in their right mind would accept it. So stick to currency 1996 and later. Most bills (except the 20 I think) have a watermark

For the coins, you'll only see the 10, 5, 2, and 1 pesos, and 50 centavos. It's somewhat common still to find coins marked with N$ for the nuevo peso. Probably since coins last so long. Wise to avoid these too, but they're unlikely to be noticed in fast transactions, probably another reason why they stick around.