When dueling, use Levicorpus on your opponent. Then, while he or she is up in 
the air, get as close as you can to them. Charge Stupefy as much as possible 
(the light from your wand will blink two times separately). Cast the charged 
Stupefy on your opponent before he or she comes back down. If done correctly, 
this will take away six of the health "dots", which is enough to completely 
defeat some opponents. Use this as many times as desired against opponents with 
more health. This will not work as well in two player dueling because your human 
opponent can wriggle free pretty quickly after being hit by Levicorpus.