Omen can actually give fulgore alot of problems. He actually beats him on the ground which @STLemonHunter can attest to as well. Fulgore loses the footsie game due to omen’s longer range normals. And locking out meter hurts Fulgore even more than other characters.
If you have trouble with gargos a good idea is to only shoot 1 or 2 fireballs at a time. Chances are you’ll get one that keeps gargos out of the sky. After that just maul him. I’d usually go pretty even vs wheels gargos with omen.