diff --git a/Spigot-Server-Patches/0502-Optimize-entity-list-iteration-requiring-entities-be.patch b/Spigot-Server-Patches/0502-Optimize-entity-list-iteration-requiring-entities-be.patch
new file mode 100644
index 0000000000..3ce498f49d
--- /dev/null
+++ b/Spigot-Server-Patches/0502-Optimize-entity-list-iteration-requiring-entities-be.patch
@@ -0,0 +1,211 @@
+From d7c73b33312bee2b2fe27b6691ad4b5ccb20a383 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <Spottedleaf@users.noreply.github.com>
+Date: Tue, 5 May 2020 19:49:23 -0700
+Subject: [PATCH] Optimize entity list iteration requiring entities be in
+ loaded chunks
+
+We retain a list of loaded entities specifically for this usage
+
+diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
+index 00dd21205d..53d3acccd3 100644
+--- a/src/main/java/net/minecraft/server/Chunk.java
++++ b/src/main/java/net/minecraft/server/Chunk.java
+@@ -801,6 +801,7 @@ public class Chunk implements IChunkAccess {
+         this.setNeighbourLoaded(0, 0, this);
+         this.loadedTicketLevel = true;
+         // Paper end - neighbour cache
++        ((WorldServer)this.world).onChunkLoad(this); // Paper - optimise entity list iteration
+         org.bukkit.Server server = this.world.getServer();
+         ((WorldServer)this.world).getChunkProvider().addLoadedChunk(this); // Paper
+         if (server != null) {
+@@ -859,6 +860,7 @@ public class Chunk implements IChunkAccess {
+         this.loadedTicketLevel = false;
+         this.resetNeighbours();
+         // Paper end
++        ((WorldServer)this.world).onChunkUnload(this); // Paper - optimise entity list iteration
+     }
+     // CraftBukkit end
+ 
+diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
+index b3785775ec..d9b3aa285a 100644
+--- a/src/main/java/net/minecraft/server/WorldServer.java
++++ b/src/main/java/net/minecraft/server/WorldServer.java
+@@ -189,6 +189,25 @@ public class WorldServer extends World {
+     }
+     // Paper end - rewrite ticklistserver
+ 
++    // Paper start - Optimize entity list iteration requiring entities be in loaded chunks
++    public final com.destroystokyo.paper.util.maplist.EntityList loadedEntities = new com.destroystokyo.paper.util.maplist.EntityList();
++    void onChunkLoad(final Chunk chunk) {
++        final com.destroystokyo.paper.util.maplist.EntityList list = chunk.entities;
++        final Entity[] entities = list.getRawData();
++        for (int i = 0, size = list.size(); i < size; ++i) {
++            this.loadedEntities.add(entities[i]);
++        }
++    }
++
++    void onChunkUnload(final Chunk chunk) {
++        final com.destroystokyo.paper.util.maplist.EntityList list = chunk.entities;
++        final Entity[] entities = list.getRawData();
++        for (int i = 0, size = list.size(); i < size; ++i) {
++            this.loadedEntities.remove(entities[i]);
++        }
++    }
++    // Paper end - Optimize entity list iteration requiring entities be in loaded chunks
++
+     // Add env and gen to constructor
+     public WorldServer(MinecraftServer minecraftserver, Executor executor, WorldNBTStorage worldnbtstorage, WorldData worlddata, DimensionManager dimensionmanager, GameProfilerFiller gameprofilerfiller, WorldLoadListener worldloadlistener, org.bukkit.World.Environment env, org.bukkit.generator.ChunkGenerator gen) {
+         super(worlddata, dimensionmanager, (world, worldprovider) -> {
+@@ -489,14 +508,13 @@ public class WorldServer extends World {
+ 
+             gameprofilerfiller.exitEnter("regular");
+             this.tickingEntities = true;
+-            ObjectIterator objectiterator = this.entitiesById.int2ObjectEntrySet().iterator();
++            Iterator<Entity> entityiterator = this.loadedEntities.iterator(); // Paper - use loaded entity list - change var name to compile fail on usage change, we need to hook remove() calls here
+ 
+             org.spigotmc.ActivationRange.activateEntities(this); // Spigot
+             timings.entityTick.startTiming(); // Spigot
+             TimingHistory.entityTicks += this.globalEntityList.size(); // Paper
+-            while (objectiterator.hasNext()) {
+-                Entry<Entity> entry = (Entry) objectiterator.next();
+-                Entity entity1 = (Entity) entry.getValue();
++            while (entityiterator.hasNext()) { // Paper - use loaded entity list
++                Entity entity1 = entityiterator.next(); // Paper - use loaded entity list
+                 Entity entity2 = entity1.getVehicle();
+ 
+                 /* CraftBukkit start - We prevent spawning in general, so this butchering is not needed
+@@ -532,7 +550,7 @@ public class WorldServer extends World {
+                 gameprofilerfiller.enter("remove");
+                 if (entity1.dead) {
+                     this.removeEntityFromChunk(entity1);
+-                    objectiterator.remove();
++                    entityiterator.remove(); this.entitiesById.remove(entity1.getId()); // Paper - use loaded entity list
+                     this.unregisterEntity(entity1);
+                 }
+ 
+@@ -1445,6 +1463,7 @@ public class WorldServer extends World {
+         if (entity instanceof EntityInsentient) {
+             this.navigators.remove(((EntityInsentient) entity).getNavigation());
+         }
++        this.loadedEntities.remove(entity); // Paper - loaded entity list
+         new com.destroystokyo.paper.event.entity.EntityRemoveFromWorldEvent(entity.getBukkitEntity()).callEvent(); // Paper - fire while valid
+         entity.valid = false; // CraftBukkit
+     }
+@@ -1514,6 +1533,11 @@ public class WorldServer extends World {
+             }
+             // Paper end
+             entity.shouldBeRemoved = false; // Paper - shouldn't be removed after being re-added
++            // Paper start - loaded entity list
++            if (this.isChunkLoaded(net.minecraft.server.MCUtil.getChunkCoordinate(entity.locX()), net.minecraft.server.MCUtil.getChunkCoordinate(entity.locZ()))) {
++                this.loadedEntities.add(entity);
++            }
++            // Paper end - loaded entity list
+             new com.destroystokyo.paper.event.entity.EntityAddToWorldEvent(entity.getBukkitEntity()).callEvent(); // Paper - fire while valid
+         }
+ 
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+index ac257d50de..995f706678 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+@@ -1110,16 +1110,16 @@ public class CraftWorld implements World {
+ 
+     @Override
+     public List<Entity> getEntities() {
+-        List<Entity> list = new ArrayList<Entity>();
++        List<Entity> list = new ArrayList<Entity>(world.loadedEntities.size()); // Paper - optimize this call
+ 
+-        for (Object o : world.entitiesById.values()) {
++        for (Object o : world.loadedEntities) { // Paper - optimize this call
+             if (o instanceof net.minecraft.server.Entity) {
+                 net.minecraft.server.Entity mcEnt = (net.minecraft.server.Entity) o;
+                 if (mcEnt.shouldBeRemoved) continue; // Paper
+                 Entity bukkitEntity = mcEnt.getBukkitEntity();
+ 
+                 // Assuming that bukkitEntity isn't null
+-                if (bukkitEntity != null && bukkitEntity.isValid()) {
++                if (bukkitEntity != null && CraftEntity.canBeSeenByPlugins(bukkitEntity)) { // Paper - optimize this call
+                     list.add(bukkitEntity);
+                 }
+             }
+@@ -1130,16 +1130,16 @@ public class CraftWorld implements World {
+ 
+     @Override
+     public List<LivingEntity> getLivingEntities() {
+-        List<LivingEntity> list = new ArrayList<LivingEntity>();
++        List<LivingEntity> list = new ArrayList<LivingEntity>(world.loadedEntities.size()); // Paper - optimize this call
+ 
+-        for (Object o : world.entitiesById.values()) {
++        for (Object o : world.loadedEntities) { // Paper - optimize this call
+             if (o instanceof net.minecraft.server.Entity) {
+                 net.minecraft.server.Entity mcEnt = (net.minecraft.server.Entity) o;
+                 if (mcEnt.shouldBeRemoved) continue; // Paper
+                 Entity bukkitEntity = mcEnt.getBukkitEntity();
+ 
+                 // Assuming that bukkitEntity isn't null
+-                if (bukkitEntity != null && bukkitEntity instanceof LivingEntity && bukkitEntity.isValid()) {
++                if (bukkitEntity != null && bukkitEntity instanceof LivingEntity && CraftEntity.canBeSeenByPlugins(bukkitEntity)) { // Paper - optimize this call
+                     list.add((LivingEntity) bukkitEntity);
+                 }
+             }
+@@ -1160,7 +1160,7 @@ public class CraftWorld implements World {
+     public <T extends Entity> Collection<T> getEntitiesByClass(Class<T> clazz) {
+         Collection<T> list = new ArrayList<T>();
+ 
+-        for (Object entity: world.entitiesById.values()) {
++        for (Object entity: world.loadedEntities) { // Paper - optimize this call
+             if (entity instanceof net.minecraft.server.Entity) {
+                 if (((net.minecraft.server.Entity) entity).shouldBeRemoved) continue; // Paper
+                 Entity bukkitEntity = ((net.minecraft.server.Entity) entity).getBukkitEntity();
+@@ -1171,7 +1171,7 @@ public class CraftWorld implements World {
+ 
+                 Class<?> bukkitClass = bukkitEntity.getClass();
+ 
+-                if (clazz.isAssignableFrom(bukkitClass) && bukkitEntity.isValid()) {
++                if (clazz.isAssignableFrom(bukkitClass) && CraftEntity.canBeSeenByPlugins(bukkitEntity)) { // Paper - optimize this call
+                     list.add((T) bukkitEntity);
+                 }
+             }
+@@ -1184,7 +1184,7 @@ public class CraftWorld implements World {
+     public Collection<Entity> getEntitiesByClasses(Class<?>... classes) {
+         Collection<Entity> list = new ArrayList<Entity>();
+ 
+-        for (Object entity: world.entitiesById.values()) {
++        for (Object entity: world.loadedEntities) { // Paper - optimize this call
+             if (entity instanceof net.minecraft.server.Entity) {
+                 if (((net.minecraft.server.Entity) entity).shouldBeRemoved) continue; // Paper
+                 Entity bukkitEntity = ((net.minecraft.server.Entity) entity).getBukkitEntity();
+@@ -1197,7 +1197,7 @@ public class CraftWorld implements World {
+ 
+                 for (Class<?> clazz : classes) {
+                     if (clazz.isAssignableFrom(bukkitClass)) {
+-                        if (bukkitEntity.isValid()) {
++                        if (CraftEntity.canBeSeenByPlugins(bukkitEntity)) { // Paper - optimize this call
+                             list.add(bukkitEntity);
+                         }
+                         break;
+diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+index ff60568ce4..f377112161 100644
+--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
++++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+@@ -180,6 +180,18 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
+         this.entity = entity;
+     }
+ 
++    // Paper start
++    // note: this does not check isChunkLoaded, use Entity#isValid to do that
++    public static boolean canBeSeenByPlugins(org.bukkit.entity.Entity entity) {
++        Entity handle = ((CraftEntity)entity).getHandle();
++        // TODO
++        // isAlive is a dumb choice, given living entities aren't alive (but are in the world) if health < 0
++        // this needs to be brought up to spigot to fix though, we are NOT breaking api implementation, especially
++        // if no-one's complained.
++        return !handle.shouldBeRemoved && handle.isAlive() && handle.valid;
++    }
++    // Paper end
++
+     @Override
+     public Chunk getChunk() {
+         net.minecraft.server.Chunk currentChunk = entity.getCurrentChunk();
+-- 
+2.26.0
+