Drawing a skull was actually surprisingly easy? I don't know how I managed to make one that looked pretty decent and believable but I'm happy I managed. I also think I got a better handle on fire this time, though the png blending modes don't look kindly upon fire.
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The weapon's burning skull sees itself. Is it a skull tormented by painful fire? Or is it a living fire caged by a physical skull? It does not know so it must scream and scream and scream.
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Shrieking Skull
Weapon (flail), rare (requires attunement)
Whenever you hit with an attack using this weapon, the target takes an extra 1d8 fire damage and the skull emits a harmless shriek that lasts for 1 minute and can be heard up to 120 feet. Additionally, if you roll the maximum value for the extra fire damage, the head of the flail deals 1d4 thunder damage to each creature of your choice within 5 feet of the original target.
Piercing Scream. While you hold this weapon, you can use an action to expend a charge and cast shatter from it targeting your own space (spell save DC 15). You are unaffected by this spell. You can’t cast this spell from the flail again until the next dawn.