They seem to be quite rare, but you might run into a special 100 peso bill in your change. The bill commemorates the 100th anniversary of the Constitution of Mexico, which was adopted in February 1917.
There is a pretty good short video on the Bank of Mexico site about the bill, and more info about the Constitution of Mexico here.
We have received a few of the bills in the bookstore, ironically mostly from visitors who got them from their bank in the USA.