That's one heck of a commit you've got there...

I may have got a bit behind with version control. A lot behind, in fact. Maybe I'll go back and split this sometime - then again, I probably won't. But hey, at least it's here!

src/main/java/electroblob/wizardry/spell/ArcaneLock.java

@@ -0,0 +1,133 @@
+package electroblob.wizardry.spell;
+
+import electroblob.wizardry.Wizardry;
+import electroblob.wizardry.util.AllyDesignationSystem;
+import electroblob.wizardry.util.NBTExtras;
+import electroblob.wizardry.util.SpellModifiers;
+import electroblob.wizardry.util.WizardryUtilities;
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.EntityLivingBase;
+import net.minecraft.entity.player.EntityPlayer;
+import net.minecraft.item.EnumAction;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.tileentity.TileEntity;
+import net.minecraft.util.EnumFacing;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.math.Vec3d;
+import net.minecraft.world.World;
+import net.minecraftforge.event.entity.player.PlayerInteractEvent;
+import net.minecraftforge.event.world.ExplosionEvent;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
+
+@Mod.EventBusSubscriber
+public class ArcaneLock extends SpellRay {
+
+	/** The NBT tag name for storing the owner's UUID in the tile entity data. */
+	public static final String NBT_KEY = "arcaneLockOwner";
+
+	public ArcaneLock(){
+		super("arcane_lock", false, EnumAction.NONE);
+	}
+
+	@Override public boolean requiresPacket(){ return true; }
+
+	@Override public boolean canBeCastByDispensers(){ return false; }
+
+	@Override public boolean canBeCastByNPCs(){ return false; }
+
+	@Override
+	protected boolean onEntityHit(World world, Entity target, Vec3d hit, EntityLivingBase caster, Vec3d origin, int ticksInUse, SpellModifiers modifiers){
+		return false;
+	}
+
+	@Override
+	protected boolean onBlockHit(World world, BlockPos pos, EnumFacing side, Vec3d hit, EntityLivingBase caster, Vec3d origin, int ticksInUse, SpellModifiers modifiers){
+		
+		if(caster instanceof EntityPlayer){
+			
+			TileEntity tileentity = world.getTileEntity(pos);
+
+			if(tileentity != null){
+
+				if(tileentity.getTileData().hasUniqueId(NBT_KEY)){
+					// Unlocking
+					if(world.getPlayerEntityByUUID(tileentity.getTileData().getUniqueId(NBT_KEY)) == caster){
+						NBTExtras.removeUniqueId(tileentity.getTileData(), NBT_KEY);
+						return true;
+					}
+				}else{
+					// Locking
+					tileentity.getTileData().setUniqueId(NBT_KEY, caster.getUniqueID());
+					return true;
+				}
+			}
+		}
+		
+		return false;
+	}
+
+	@Override
+	protected boolean onMiss(World world, EntityLivingBase caster, Vec3d origin, Vec3d direction, int ticksInUse, SpellModifiers modifiers){
+		return false;
+	}
+
+	@SubscribeEvent
+	public static void onLeftClickBlockEvent(PlayerInteractEvent.LeftClickBlock event){
+
+		if(!canBypassLocks(event.getEntityPlayer())){
+
+			TileEntity tileentity = event.getWorld().getTileEntity(event.getPos());
+
+			// Prevents arcane-locked containers from being broken
+			// Need to check if it has the unique id first because if it is absent getUniqueId will return the nil UUID
+			if(tileentity != null && tileentity.getTileData().hasUniqueId(ArcaneLock.NBT_KEY)){
+				// Only the player that owns the lock may break the container
+				// If nobody owns it (i.e. it's part of a shrine), player will be null
+				// Why is getUniqueId marked @Nullable? It literally creates a UUID and returns it!
+				if(event.getEntityPlayer().getUniqueID() != tileentity.getTileData().getUniqueId(ArcaneLock.NBT_KEY)){
+					event.setCanceled(true);
+				}
+			}
+		}
+	}
+
+	@SubscribeEvent
+	public static void onRightClickBlockEvent(PlayerInteractEvent.RightClickBlock event){
+
+		if(!canBypassLocks(event.getEntityPlayer())){
+
+			TileEntity tileentity = event.getWorld().getTileEntity(event.getPos());
+
+			// Prevents arcane-locked containers from being opened
+			// Need to check if it has the unique id first because if it is absent getUniqueId will return the nil UUID
+			if(tileentity != null && tileentity.getTileData().hasUniqueId(ArcaneLock.NBT_KEY)){
+				// Why is getUniqueId marked @Nullable? It literally creates a UUID and returns it!
+				EntityPlayer owner = event.getWorld().getPlayerEntityByUUID(tileentity.getTileData().getUniqueId(ArcaneLock.NBT_KEY));
+				// Only the player that owns the lock or an ally of that player may open the container
+				// If nobody owns it (i.e. it's part of a shrine, or the owner logged out), player will be null
+				// Unfortunately we can't get the owner's allies if the owner is offline
+				// Perhaps if this crops up again we can store inverted 'ally of' maps as well?
+				if(owner == null || (owner != event.getEntityPlayer() && !AllyDesignationSystem.isPlayerAlly(owner, event.getEntityPlayer()))){
+					event.setCanceled(true);
+				}
+			}
+		}
+	}
+
+	private static boolean canBypassLocks(EntityPlayer player){
+
+		if(!player.isCreative()) return false;
+		if(Wizardry.settings.creativeBypassesArcaneLock) return true;
+		MinecraftServer server = player.world.getMinecraftServer();
+		return server != null && WizardryUtilities.isPlayerOp(player, server);
+	}
+
+	@SubscribeEvent
+	public static void onExplosionEvent(ExplosionEvent.Detonate event){
+		// Prevents arcane-locked containers from being exploded
+		event.getAffectedBlocks().removeIf(pos -> event.getWorld().getTileEntity(pos) != null
+				&& event.getWorld().getTileEntity(pos).getTileData().hasUniqueId(NBT_KEY));
+	}
+
+}