Any licensing is between the user and the creator (to protect the creator's property just as much as the user). So, a few things:
For assets, we use Copyright Law.
Itch provides the options to link to Creative Commons (a service with preset licence arrangements) that the creator can link to, or the creator can reserve some or all rights, and I would need to include a document in the download files telling you your explicit permissions. But Itch doesn't send their legal team to handle any grievance I would have with you, or vice versa.
With that in mind:
In this case, with these cards, I WANT you to be able to use them, and I want you to feel good trying to make something of yourself with them if you have a DYNAMITE idea. So, they are royalty-free and can be used in commercial work without further permissions within the VERY LOOSE standards of the licence.
Creative Commons has written public licences for different levels of courtesy where all you have to do to "AVOID THE COURTS" is:
Attribute me (as GREEBLES, or DevlynJD).
DO NOT CHANGE THE ART or make derivatives. (E.G. no vegetables in place of the swords.)
This licence allows for commercial use.
"Do not directly post the asset pack on some shady dark-web place like Etsy saying it is yours and you made this" is the only protection I'm seeking.
Here is the link to review this specific licence:
For future worries, troubles, or doubts:
Simply typing in the comments is a form of written correspondence and as such holds a bit of legal weight; if you and I have an exchange about, say, VEGETABLE DERIVATIVES, it is archival and retrievable. It isn't ironclad, but if I did go to the court and say you done me wrong by putting veggies in my art and you show Mr.Dr.Judgeman a comment where I said you COULD use vegetables in my art, you would win. So... in case we ever get there...
You, USER GEHGA, and YOU ALONE, have permission to add VEGETABLES to any of the HEART, SPADE, DIAMOND, and/or CLUB cards. The BLM cards are not allowed to be modified.
Whether I write it here or in a simple text doc won't change that I'M NOT GONNA COME AFTER YOU WITH MY CRACK EXPERT LEGAL TEAM. I do have a lawyer; he's a nine-years-old, but a legend in the civil circuit.
Thanks for being interested enough to seek legal protections! This is a good and scary feeling!
Please point me at your work if you decide to go forward with it (SO I CAN REVIEW IT, EVISCERATE IT, AND EAT ITS BABIES).
PS: I'll see you in court.