It's looking really great but I think these little ghosts are unnecessary. If you would like to keep these ghosts, I think reducing the amount of them would improve on the overall look.
Also you can try replace these ghosts with thunder effect behind the skull. Just an idea I had in mind while typing all this. Overall, I really like this.

I really dig the purple/green one.

Those just look really nice.

@Shep Thank you for your feedback! I'll look into it; it'll be a little tricky to make the skull "less transparent" since it's fully opaque / alpha has a value of 255, perhaps an outlining cloud particle should help it pop out more.

I like the concept and the design of the skull, I just feel perhaps it's the super bright color makes it difficult to distinguish the details. At most ranges it will look like just a bright green/purple/orange version of Gravelly Ghoul.

My suggestion would be to make the effect larger and the Skull less transparent so that the awesome details can be seen in greater detail. I would also say to make the clouds look less bright, and make them more realistic sort of like the ones in Morning Glory except of course halloween colored.

as long as this dosen't become the all their is on a hat from a crate/case then yes it would be fine as along as every crate/case has it

@Squidge Thank you very much! I do have a few surprises in store for you

This is great! I saw your witching hour set of effects when they came out and fell in love then I saw this one, makes me wonder what other effects similar to this and witching hour you may make. Even if you don't, excited to see what else you make and I hope it gets in this halloween!