diff --git a/packages/ecs/src/ecs.js b/packages/ecs/src/ecs.js
index 6eafc8e..1e06cda 100644
--- a/packages/ecs/src/ecs.js
+++ b/packages/ecs/src/ecs.js
@@ -77,7 +77,7 @@ export default class Ecs {
 
     }
     const wrappedSystem = new WrappedSystem(this.Components);
-    wrappedSystem.reindex(Object.keys(this.$$entities));
+    wrappedSystem.reindex(this.entities);
     this.$$systems.push(wrappedSystem);
   }
 
@@ -87,7 +87,7 @@ export default class Ecs {
   }
 
   createExact(entity, components) {
-    this.createManyExact([entity, components]);
+    this.createManyExact([[entity, components]]);
   }
 
   createMany(componentsList) {
@@ -139,7 +139,7 @@ export default class Ecs {
       let components = {};
       let entity;
       if (Array.isArray(entities[i])) {
-        [entity, components] = entities[i];
+        [entity, components = {}] = entities[i];
       }
       else {
         entity = entities[i];
@@ -213,7 +213,7 @@ export default class Ecs {
   }
 
   destroyAll() {
-    this.destroyMany(Object.keys(this.$$entities).map((entity) => BigInt(entity)));
+    this.destroyMany(this.entities);
   }
 
   destroyMany(entities) {
@@ -291,6 +291,14 @@ export default class Ecs {
     view.setUint32(0, entitiesWritten, true);
   }
 
+  get entities() {
+    const entities = [];
+    for (const i in this.$$entities) {
+      entities.push(BigInt(i));
+    }
+    return entities;
+  }
+
   get(entity) {
     if (!this.$$entities[entity]) {
       return undefined;
@@ -420,7 +428,10 @@ export default class Ecs {
     }
   }
 
-  tickFinalize() {
+  tickFinalize(elapsed) {
+    for (let i = 0; i < this.$$systems.length; i++) {
+      this.$$systems[i].finalize(elapsed);
+    }
     this.tickDestruction();
     this.setClean();
   }
diff --git a/packages/ecs/src/system.js b/packages/ecs/src/system.js
index 126bbea..eaf9136 100644
--- a/packages/ecs/src/system.js
+++ b/packages/ecs/src/system.js
@@ -31,6 +31,9 @@ export default class System {
     }
   }
 
+  // eslint-disable-next-line class-methods-use-this
+  finalize() {}
+
   static normalize(SystemLike) {
     if (SystemLike.prototype instanceof System) {
       return SystemLike;
@@ -62,4 +65,7 @@ export default class System {
     this.destroying = [];
   }
 
+  // eslint-disable-next-line class-methods-use-this
+  tick() {}
+
 }
diff --git a/packages/ecs/test/ecs.js b/packages/ecs/test/ecs.js
index b46c6a5..952bf9d 100644
--- a/packages/ecs/test/ecs.js
+++ b/packages/ecs/test/ecs.js
@@ -1,4 +1,3 @@
-/* eslint-disable react/prefer-stateless-function */
 import {expect} from 'chai';
 
 import Bundle from '../src/bundle';