Negative amount of skulls?No Thanks
I know that
"skull.human": "1/1",
  "skull.wolf": "1/1"​

does that there's only 1 skull out of a body instead of 2x/5x or whatever.
Now I have Leveling activated on my server and 2x Gather Control and the skulls do appear 3x now 'cause of leveling.
So, I was wondering if I could somehow give it a negative amount to prevent this and only have one skull again.
Like "skull.human": "-1/-1" or something?

Using multiple plugins that perform a single function always causes a conflict.In the case of resource extraction, each plugin multiplies the number of resources by a given value in it in turn.Plugins run in alphabetical order.You need to look at the settings of the plugin responsible for the levels.
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