Doesn’t look like the typical Fuel Rod explosion. It also has effected the blue spartan to the left of it and seems like there is a green aura around him.
Promethean grenade?
> Promethean grenade?
No we’ve seen that in the spartan ops vids. Thats more yellow/beige, this is obviously green like the fuel rod gun.
Good find OP
It’s… Green…
'nuff said.
Could be FRG… Looks like an awesome green mess. 
I’m loving the saw. (The UNSC LMG)
Tear grenade
lego
It’s hard to say, but my guess is (weapon-wise) that it’s a new type of 'nade.
However, I have heard that during Beta versions of games (especially Halo), the smoke/haze effects can be different colors than the usual and surrounding environments, so it could possibly be a typical frag grenade.
If the regen field is anything like it was in halo 3, this might be it.
That’s not a weapon, it’s a Regen Field (I think).
It looks more smokey-like and not really compact like the regen.
> http://i56.photobucket.com/albums/g178/Pr1v4t3/green.png
>
> Doesn’t look like the typical Fuel Rod explosion. It also has effected the blue spartan to the left of it and seems like there is a green aura around him.
Is anybody else looking at the weird hologram thing on the left? Is that a hologram, or something more sinister…
> It looks more smokey-like and not really compact like the regen.
Looking at it again, I agree.
Well, fuel rod with acid clouds? corrosive area effect?
The green cloud that follows the player got to have some deeper meaning…
Looks like Regen as some of the green mist is getting around the player’s armor.