I have a 5x server. And I have the Trophy Signs plugin which lets people create a trophy made out of the skull of killed players.
The problem is that every players dead body puts out 5 skulls. Same with the wolves btw.
What can I do that a body has only 1 skull?

Try use this from description:

      "CustomRateMultResource": { /* adjusting the multipliers for a particular item for resource extraction */
        "stones": "3/4",
        "sulfur.ore": "3/4"
      },​​

So, like this:

      "CustomRateMultResource": {
        "skull.human": "1/1",
        "skull.wolf": "1/1"
      },

Rust items

That did it. Very helpful. Thank you.