ItemCount(/[series/]/[season/])
Will tell you how many episodes are in a season of a TV show.
ItemCount(/[series/]/[episode/])
Will tell you how many episodes total you have of a specific show
I've been playing with this one in an attempt get a count of the amount of seasons that I have for a show.
itemcount(if/(isequal/(/[Episode/]/, 1/, 1/)/, /[Series/]/,/))
For every episode 1 you have of a series it will return that total. So, if you have 5 seasons of a show, each starting with episode #1 it will return 5. For every other episode it will return the grand total of all episodes in your library that aren't episode 1.
itemcount(/[series/]if/(isequal/(/[Episode/]/, 1/, 1/)/, /[Series/]/,/))
Pretty much the same as the last one, it has the same behavior for episode 1 but the other episodes will show you the total episodes you have for that specific series. Not sure how useful either of these are, I was just experimenting.
ItemCount(/[artist/])
Tells you how many tracks you have from a specific artist.
ItemCount(albumkey/(/))
How many tracks are on a single album
ItemCount(albumkey/(/)/[disc #/])
How many tracks are on each disc of a set.