Are there numbers bigger than myrillion?

A "myrillion" is not an actual number, just a made-up name.

In any case, for any number, there are always larger numbers. For example, if you add one to a million, you get a number that is larger than a million. If you choose to define a "myrillion" to be a 1 with so-and-so many zeroes, just add one to it, or add an additional zero, and you get a number that is even larger.