org.bukkit.command.CommandException: Unhandled exception executing command 'mm' in plugin MythicMobs v4.9.1-3295
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot.jar:git-Spigot-db6de12-18fbb24]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot.jar:git-Spigot-db6de12-18fbb24]
        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:641) ~[spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.PlayerConnection.handleCommand(PlayerConnection.java:1162) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:997) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(PacketPlayInChat.java:45) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(PacketPlayInChat.java:1) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_144]
        at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_144]
        at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:715) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557) [spigot.jar:git-Spigot-db6de12-18fbb24]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_144]
Caused by: java.lang.NoClassDefFoundError: org/bukkit/attribute/Attribute
        at io.lumine.xikage.mythicmobs.mobs.MythicMob.applyMobOptions(MythicMob.java:810) ~[?:?]
        at io.lumine.xikage.mythicmobs.mobs.ActiveMob.setLevel(ActiveMob.java:252) ~[?:?]
        at io.lumine.xikage.mythicmobs.mobs.MythicMob.spawn(MythicMob.java:728) ~[?:?]
        at io.lumine.xikage.mythicmobs.mobs.MobManager.spawnMob(MobManager.java:536) ~[?:?]
        at io.lumine.xikage.mythicmobs.mobs.MobManager.spawnMob(MobManager.java:525) ~[?:?]
        at io.lumine.xikage.mythicmobs.commands.mobs.SpawnCommand.onCommand(SpawnCommand.java:150) ~[?:?]
        at io.lumine.xikage.mythicmobs.utils.commands.Command.onCommand(Command.java:68) ~[?:?]
        at io.lumine.xikage.mythicmobs.utils.commands.Command.onCommand(Command.java:59) ~[?:?]
        at io.lumine.xikage.mythicmobs.utils.commands.Command.onCommand(Command.java:59) ~[?:?]
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot.jar:git-Spigot-db6de12-18fbb24]
        ... 15 more