Introduce "BackFireShrapnelWarhead" from MW

[dnqbob]

I think this warhead is pretty useful on create some visual/gameplay effect.

1. blood/energy sucker like the vampire in MW. Attack will let victim generate a backfire weapon that heal/power the attacker, with good visual feedback.

2. Classic boomerang based weapon for both ancient/modern warfare. Backfire weapon provides a visual feedback, and a condition of reload ammo. It can be used for boomerang or a robot fire part of its body as weapon and take it back after hit. (also a hidden effect of the longer the attack range, the slower the reload time for flying back)

3. used to make reverse projectile visual effect, used with instant hit. like gravity/magnet drag the enemy instead of push enemy in visual.