Halo 3 odst firefight special skull unlock?

Games Other Halo
1

Hey everyone!

I was looking through some profiles lately and I came across:
Tsxki

Now if you look at this guys Halo 3 ODST service record he has a flaming skull for the firefight skull and I was wondering if anyone knows how to get that? I reached out but haven’t heard back and other profiles I looked at who completed their highest score on legendary still don’t have the flaming skull icon. Appreciate the help!

2

I went to see your profile and you managed to unblock it, congratulations to you.

3

how did you manage to unlock it?

4

Thank Tsxki!

5

What special skull is this?