To kill a decepticon, you must deliver a massive thrust punch.
As an without, if the decepticon survives a punch, try picking
something up and toss it right at him or her. You can either use
your cannons or other weapons to blast a decepticon away. Use your
fists and knuckles to deliver an incredibly powerful punch to the
decepticon, this will cause a lot of damage to the decepticon. If
the he or she is still live, try to pick him or her up and toss
him/her down to the ground square as you can. Just deliver flying
bullets to the decepticon's eyes, that will blind their eyes and
will also give you a much easier chance to break the decepticon's
face. If the decepticon sees your attacks, he or she will block
your attacks and will try to kill you. Spraying flying bullets to
the decepticon's eyes will make the decepticon unable to see your
attacks and will not block your attacks. After you've delivered
some flying bullets to the decepticon's eyes, grab the decepticon's
head using your left hand and raise your right hand up. Get your
fists and knuckles ready. Slam your right hand to the decepticon's
face extremely hard and fast with your fists and knuckles aiming at
the decepticon's face .That will cause instant death to the
decepticon. Remember that the decepticon leader, Megatron got his
face broken by Optimus Prime. So see how did Optimus Prime break
Megatron's face then you'll find out how to defeat a
decepticon.