Hello, I am a bit new to mods so I am not very sure why my server crashes when using the knives that the mod gives, that is, when I use them on myself it does not give a problem but when I use them Against another person the game crashes and I don't know what to do to solve the problem, I would appreciate any help, thank you.

Should be fixed now in v5.6.8, let me know if it's still an issue.

Could you provide a crash log for me to look at? And is there any other mods installed?

The crash log:
[15:47:04] [Server thread/FATAL] [net.minecraft.server.MinecraftServer]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_292]
at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_292]
at net.minecraft.util.Util.func_181617_a(SourceFile:47) [h.class:?]
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:926) [MinecraftServer.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:461) [nz.class:?]
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:865) [MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:737) [MinecraftServer.class:?]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_292]
Caused by: java.lang.NullPointerException
at sorazodia.cannibalism.config.JSONConfig.checkEntity(JSONConfig.java:199) ~[JSONConfig.class:?]
at sorazodia.cannibalism.items.ItemKnife.func_111207_a(ItemKnife.java:157) ~[ItemKnife.class:?]
at net.minecraft.item.ItemStack.func_111282_a(ItemStack.java:453) ~[aip.class:?]
at net.minecraft.entity.player.EntityPlayer.func_190775_a(EntityPlayer.java:1302) ~[aed.class:?]
at net.minecraft.network.NetHandlerPlayServer.func_147340_a(NetHandlerPlayServer.java:1818) ~[pa.class:?]
at net.minecraft.network.play.client.CPacketUseEntity.func_148833_a(SourceFile:69) ~[li.class:?]
at net.minecraft.network.play.client.CPacketUseEntity.func_148833_a(SourceFile:13) ~[li.class:?]
at net.minecraft.network.PacketThreadUtil.lambda$checkThreadAndEnqueue$0(PacketThreadUtil.java:14) ~[hv.class:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_292]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_292]
at net.minecraft.util.Util.func_181617_a(SourceFile:46) ~[h.class:?]
... 5 more

And I also have other mods installed

Could you provide a crash log for me to look at? And is there any other mods installed?

It's a bug. I recon you cannot do anything untill a fix is released.

@SoraZodia the crash is at JSONConfig.checkEntity. A null check is missing, should be easy to fix. Let me know if you need help with this, I could try to greate a PR.

mc_1  | java.util.concurrent.ExecutionException: java.lang.NullPointerException
mc_1  |         at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_212]
mc_1  |         at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_212]
mc_1  |         at net.minecraft.util.Util.func_181617_a(SourceFile:47) [h.class:?]
mc_1  |         at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:723) [MinecraftServer.class:?]
mc_1  |         at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:397) [nz.class:?]
mc_1  |         at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668) [MinecraftServer.class:?]
mc_1  |         at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526) [MinecraftServer.class:?]
mc_1  |         at java.lang.Thread.run(Thread.java:748) [?:1.8.0_212]
mc_1  | Caused by: java.lang.NullPointerException
mc_1  |         at sorazodia.cannibalism.config.JSONConfig.checkEntity(JSONConfig.java:199) ~[JSONConfig.class:?]
mc_1  |         at sorazodia.cannibalism.items.ItemKnife.func_111207_a(ItemKnife.java:157) ~[ItemKnife.class:?]
mc_1  |         at net.minecraft.item.ItemStack.func_111282_a(ItemStack.java:391) ~[aip.class:?]
mc_1  |         at net.minecraft.entity.player.EntityPlayer.func_190775_a(EntityPlayer.java:1220) ~[aed.class:?]
mc_1  |         at net.minecraft.network.NetHandlerPlayServer.func_147340_a(NetHandlerPlayServer.java:1075) ~[pa.class:?]
mc_1  |         at net.minecraft.network.play.client.CPacketUseEntity.func_148833_a(SourceFile:69) ~[li.class:?]
mc_1  |         at net.minecraft.network.play.client.CPacketUseEntity.func_148833_a(SourceFile:13) ~[li.class:?]
mc_1  |         at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13) ~[hv$1.class:?]
mc_1  |         at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_212]
mc_1  |         at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_212]
mc_1  |         at net.minecraft.util.Util.func_181617_a(SourceFile:46) ~[h.class:?]```