I was thinking, perhaps 343 can do a flaming floating skull with flame for anyone who beats Halo 5 SLASO (Solo Legendary All Skulls On) mode.
or perhaps have an all skin loadout of a pile of skulls, facing towards the muzzle of the gun with a sill frame orange flame that glow and pulse slowly.
Or simply just have a armor that makes the head go on fire like the classic Halo 3 way.
If you complete the campaign on SLASO you should get a pack called the “Mythical Spartan” Req pack where you get ALL mythic reqs/certs that were in the game at launch and ONLY the ones at launch so you still have to unlock the newer mythics.