Step 1: Equip a Burning Flail, with the Cruciform Firebox or, preferably, Dressad’s Roaster illusion equipped.
Step 2: Hold your first and second heavy attack, you can clearly see a fire trail effect, as pictured here. You can release some heavies, as well, and throw some lights, to see all of the fire trail effects in question.
Step 3: Go to crafting, and change the illusion on your flail to The Brass Flail.
Step 4: Repeat step 2. Notice how it has neither the normal fire trail on the lights, nor the smooth fire trail on the heavies.
I have been able to reproduce this several times, across full restarts of vermintide, and my pc, with the Cruciform Firebox and Dressad’s Roaster working every time, while The Brass Flail has no visual effect any time. This is especially strange, considering the fact that The Brass Flail is a modified version of Dressad’s Roaster, with blue glowing runes added onto it.
Below are The Brass Flail’s held heavies,
Its released heavies,
its lights,
And its push attack.
For comparison, below are the Dressad’s Roaster held heavies,
Its released heavies,
its lights,
And its push attack.
And for the sake of completion, below are the Cruciform Firebox’s held heavies,
its released heavies,
its lights,
and its push attack.
I hope this is not intentional, as I am quite fond of the fire effects, especially the smoother fire effect on the heavies. If you have any more questions, be sure to let me know.