So I was watching my brother play CoD W@W and there was some guy with invincibility who could fly around, and take on a tank along with the whole team. So I was trying to figure out how he did it, I told my brother to take a bouncing betty and hold down the trigger for it, then he got stabbed by an enemy and instantly went from around 55 to 65. I don't know if it's instant for lower levels, but it was a ton of xp, around 10 million or something.