For example, she used magic missile but she was able to cross magic missile with firebolt to have three guaranteed hit fire darts to creatures with weakness to fire. Alternatively, she could have taken the damage potential of firebolt with ranged attack but x3. There is a small chance of it being weaker and rolling a 1 will cause unpredictable results. Rolling 20 will cause critical hits or something else beneficial in addition. You will describe what you want the spell to do, it's not a random combination, but it may be limited.
