retval=SkillTarget(thing, source, param0, param1);
retval: In singleplayer, any value returned by ReturnEx() in the skill message will be assigned to retval. But SkillTarget() does not return a value from other computers.
source: This value becomes the sourceref of the skill message.
param0: This value is the first param of the skill message.
param1: This is the second param.