In sandbox, type TAB to enter a command
Just type the spell name and press ENTER (e.g. shock bomb, mud ball, fissure, ...) The spell is thrown at the direction of your cursor
You can set the power with which you throw a spell using the command power.NUMBER
where NUMBER
is a number between 50
and 2000
Every spell that you cast after setting a specific power, will be thrown at that power.