Card: Mutilate
Type: Spell
Text: All creatures get -X/-X until end of turn. X is the number of Black gems.
The discussion title pretty much describes the bug and it should be easy to reproduce.
Hello @Anonymous2112 ,
Thank you for all the information provided, this issue will be investigated!
If you have any additional information that you consider relevant, please don’t hesitate to send me 
Rebeca.