public static void InputActiviateSkill(int index)
 {
     if(skills[index] != null && !skills[index].passive)//cannot activate a passive skill by input
     {
         skill_to_cast = skills[index];
         skill_to_cast.Activiate();
     }
 }
 protected void StartSkill(Skill s)
 {
     ai.current_skill = s;
     s.Activiate();
 }