Stack trace here.
[15:01:55] [Spigot Watchdog Thread/ERROR]: The server has stopped responding!
[15:01:55] [Spigot Watchdog Thread/ERROR]: Please report this to http://www.spigotmc.org/
[15:01:55] [Spigot Watchdog Thread/ERROR]: Be sure to include ALL relevant console errors and Minecraft crash reports
[15:01:55] [Spigot Watchdog Thread/ERROR]: Spigot version: git-Spigot-1496 (MC: 1.7.9)
[15:01:55] [Spigot Watchdog Thread/ERROR]: ------------------------------
[15:01:55] [Spigot Watchdog Thread/ERROR]: Server thread dump (Look for plugins here before reporting to Spigot!):
[15:01:55] [Spigot Watchdog Thread/ERROR]: ------------------------------
[15:01:55] [Spigot Watchdog Thread/ERROR]: Current Thread: Server thread
[15:01:55] [Spigot Watchdog Thread/ERROR]: PID: 13 | Suspended: false | Native: false | State: RUNNABLE
[15:01:55] [Spigot Watchdog Thread/ERROR]: Stack:
[15:01:55] [Spigot Watchdog Thread/ERROR]: java.util.HashMap.getEntry(HashMap.java:469)
[15:01:55] [Spigot Watchdog Thread/ERROR]: java.util.HashMap.get(HashMap.java:421)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.java.JavaPluginLoader.getClassByName(JavaPluginLoader.java:182)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:73)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:62)
[15:01:55] [Spigot Watchdog Thread/ERROR]: java.lang.ClassLoader.loadClass(ClassLoader.java:425)
[15:01:55] [Spigot Watchdog Thread/ERROR]: java.lang.ClassLoader.loadClass(ClassLoader.java:358)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.Util.(Util.java:37)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.BarAPI.addDragon(BarAPI.java:421)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.BarAPI.getDragon(BarAPI.java:417)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.BarAPI.setMessage(BarAPI.java:223)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.ThaH3lper.com.Mobs.BarCountdown.run(BarCountdown.java:44)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.ThaH3lper.com.Mobs.MobHandler.BossHitByPlayer(MobHandler.java:61)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.ThaH3lper.com.Listener.MobDamaged.MobDamagedEvent(MobDamaged.java:26)
[15:01:55] [Spigot Watchdog Thread/ERROR]: sun.reflect.GeneratedMethodAccessor675.invoke(Unknown Source)
[15:01:55] [Spigot Watchdog Thread/ERROR]: sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[15:01:55] [Spigot Watchdog Thread/ERROR]: java.lang.reflect.Method.invoke(Method.java:606)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:292)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:47)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.event.CraftEventFactory.callEvent(CraftEventFactory.java:99)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:424)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:451)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.EntityLiving.damageEntity(EntityLiving.java:665)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.EntityMonster.damageEntity(EntityMonster.java:48)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.entity.CraftLivingEntity.damage(CraftLivingEntity.java:203)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.targeted.PainSpell.causePain(PainSpell.java:95)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.targeted.PainSpell.castAtEntity(PainSpell.java:110)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.targeted.AreaEffectSpell.doAoe(AreaEffectSpell.java:150)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.targeted.AreaEffectSpell.castAtLocation(AreaEffectSpell.java:190)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.Subspell.castAtLocationReal(Subspell.java:219)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.Subspell.castAtLocation(Subspell.java:189)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.TargetedMultiSpell.castTargetedSpell(TargetedMultiSpell.java:202)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.TargetedMultiSpell.runSpells(TargetedMultiSpell.java:166)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.TargetedMultiSpell.castAtEntity(TargetedMultiSpell.java:146)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.Subspell.castAtEntityReal(Subspell.java:166)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.Subspell.castAtEntity(Subspell.java:136)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.PassiveSpell.activateSpells(PassiveSpell.java:183)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.PassiveSpell.activate(PassiveSpell.java:142)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.PassiveSpell.activate(PassiveSpell.java:129)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.spells.passive.GiveDamageListener.onDamage(GiveDamageListener.java:90)
[15:01:55] [Spigot Watchdog Thread/ERROR]: sun.reflect.GeneratedMethodAccessor847.invoke(Unknown Source)
[15:01:55] [Spigot Watchdog Thread/ERROR]: sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[15:01:55] [Spigot Watchdog Thread/ERROR]: java.lang.reflect.Method.invoke(Method.java:606)
[15:01:55] [Spigot Watchdog Thread/ERROR]: com.nisovin.magicspells.MagicSpells$1.execute(MagicSpells.java:860)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:47)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.event.CraftEventFactory.callEvent(CraftEventFactory.java:99)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:424)
[15:01:55] [Spigot Watchdog Thread/ERROR]: org.bukkit.craftbukkit.v1_7_R3.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:451)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.EntityLiving.damageEntity(EntityLiving.java:665)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.EntityMonster.damageEntity(EntityMonster.java:48)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.EntityZombie.damageEntity(EntityZombie.java:164)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.EntityHuman.attack(EntityHuman.java:930)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.PlayerConnection.a(PlayerConnection.java:1159)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.PacketPlayInUseEntity.a(SourceFile:55)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.PacketPlayInUseEntity.handle(SourceFile:10)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.NetworkManager.a(NetworkManager.java:180)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.ServerConnection.c(ServerConnection.java:81)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.MinecraftServer.v(MinecraftServer.java:720)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:283)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:583)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:489)
[15:01:55] [Spigot Watchdog Thread/ERROR]: net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.Util.(Util.java:37)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.BarAPI.addDragon(BarAPI.java:421)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.BarAPI.getDragon(BarAPI.java:417)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.confuser.barapi.BarAPI.setMessage(BarAPI.java:223)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.ThaH3lper.com.Mobs.BarCountdown.run(BarCountdown.java:44)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.ThaH3lper.com.Mobs.MobHandler.BossHitByPlayer(MobHandler.java:61)
[15:01:55] [Spigot Watchdog Thread/ERROR]: me.ThaH3lper.com.Listener.MobDamaged.MobDamagedEvent(MobDamaged.java:26)
The problem doesn't come from MagicSpells.