%{mousey} and %{mousex} are correct syntax, but in order for them to be parsed, you either have to use them inside an actual mzscript, or, you have to prefix what you're doing with !exec (that tells the mzvars to be expanded).

So, something like: !exec !MoveMouse %{mousex} %#%{mousey} - 20%#

The %#...%# is necessary to make it perform the math operation.

For the rainmeter replacement: xStatsGraph