I have recently discovered a way to get Invincibility 
on multi player the way to get it is. first you must 
pick a level with portals and scorpian launchers and 
a friend that is kind enough to do this for you ok now 
first tell your friend to get a scorpian launcher and 
meet you at the portal than go to the portal you stand 
directely in front of the portal then have him take your 
energy out to about ten of fifteen then while standing 
directely in front of the portal have him shoot you into 
the portal with a scorpian launcher and your friend will 
get a kill every time you go through the portal and come 
out if he shoots you. you will have 0 energy for ever 
unless you get any health so dont get health. I recommend 
doing this on Tellaportastic level!