Hello,
My question is fairly simple. I'm wondering if it's possible to create magic mobs riding something, for example the baby zombie on a chicken or the skeleton on a spider. If this is possible, how do I do this? If it's not, could this be added?

I've added some options to SpawnEntity that will allow this. You'll need the latest dev build. See the piggyback example spell:

https://github.com/elBukkit/MagicPlugin/blob/master/Magic/src/main/resources/examples/survival/spells/piggyback.yml

Ahh thanks!! Great!