Don't make a new metadata value for every block every time.

src/main/java/com/gmail/nossr50/listeners/BlockListener.java

@@ -18,7 +18,6 @@ import org.bukkit.event.block.BlockPistonExtendEvent;
 import org.bukkit.event.block.BlockPistonRetractEvent;
 import org.bukkit.event.block.BlockPlaceEvent;
 import org.bukkit.inventory.ItemStack;
-import org.bukkit.metadata.FixedMetadataValue;
 
 import com.gmail.nossr50.mcMMO;
 import com.gmail.nossr50.config.AdvancedConfig;
@@ -62,13 +61,14 @@ public class BlockListener implements Listener {
      */
     @EventHandler(priority = EventPriority.MONITOR)
     public void onBlockPistonExtend(BlockPistonExtendEvent event) {
+
         List<Block> blocks = event.getBlocks();
         BlockFace direction = event.getDirection();
         Block futureEmptyBlock = event.getBlock().getRelative(direction); // Block that would be air after piston is finished
 
         for (Block b : blocks) {
             if (mcMMO.placeStore.isTrue(b)) {
-                b.getRelative(direction).setMetadata("pistonTrack", new FixedMetadataValue(plugin, true));
+                b.getRelative(direction).setMetadata(mcMMO.blockMetadataKey, mcMMO.blockMetadata);
                 if (b.equals(futureEmptyBlock)) {
                     mcMMO.placeStore.setFalse(b);
                 }
@@ -76,9 +76,9 @@ public class BlockListener implements Listener {
         }
 
         for (Block b : blocks) {
-            if (b.getRelative(direction).hasMetadata("pistonTrack")) {
+            if (b.getRelative(direction).hasMetadata(mcMMO.blockMetadataKey)) {
                 mcMMO.placeStore.setTrue(b.getRelative(direction));
-                b.getRelative(direction).removeMetadata("pistonTrack", plugin);
+                b.getRelative(direction).removeMetadata(mcMMO.blockMetadataKey, plugin);
             }
         }
     }

src/main/java/com/gmail/nossr50/listeners/EntityListener.java

@@ -301,10 +301,7 @@ public class EntityListener implements Listener {
      */
     @EventHandler (priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onCreatureSpawn(CreatureSpawnEvent event) {
-        if (Misc.isSpawnerXPEnabled) {
-            return;
-        }
-        else if (event.getEntity() == null) {
+        if (Misc.isSpawnerXPEnabled || event.getEntity() == null) {
             return;
         }
 

src/main/java/com/gmail/nossr50/mcMMO.java

@@ -94,6 +94,10 @@ public class mcMMO extends JavaPlugin {
     public static FixedMetadataValue entityMetadata;
     public final static String entityMetadataKey = "mcMMO: Spawned Entity";
 
+    // Block Metadata Values
+    public static FixedMetadataValue blockMetadata;
+    public final static String blockMetadataKey = "mcMMO: Piston Tracking";
+
     /**
      * Things to be run when the plugin is enabled.
      */
@@ -102,7 +106,9 @@ public class mcMMO extends JavaPlugin {
         try {
             p = this;
             getLogger().setFilter(new LogFilter(this));
-            entityMetadata = new FixedMetadataValue(mcMMO.p, true);
+            entityMetadata = new FixedMetadataValue(this, true);
+            blockMetadata = new FixedMetadataValue(this, true);
+
             setupFilePaths();
             setupSpout();
             loadConfigFiles();