Sheila;
Generally, the .22 magnum (rimfire) is not considered a "powerful" round, when compared to the various centerfire rounds available.
It is a very useful round however, and is powerful enough for clean kills on woodchucks, coon, and fox..
Within decent range, I would use it on our eastern coyotes.
As far as the Marlin in .22 magnum..that is an excellent choice..they are accurate and dependable.
..Just my two cts...