The Kill Counter addon has two different versions: Player kills and Mob kills. The Player kills addon WILL NOT WORK if you have another addon with a player entity script with a priority higher than the Kill Counter addon. If the Kill Counter addon has a higher priority, then the other addon will not work, so if you’re having problems with a world with multiple packs, that might be why.
Next, put down a repeating command block, set to always active, with the command: /function kill.
After you’ve done this, the kills will be counted!
You MAY alter my code to fit your game better, but DON’T upload it anywhere except in the comments down below, if you think others may benefit from it.
You MAY look at my code to see how to make a kill counter of your own, and if you do make one, you MAY upload it, unless it’s a copy/near copy of my addon, and if you DO make a unique addon, please give me credit for the basic mechanics.