diff --git a/app/ecs/ecs.js b/app/ecs/ecs.js
index 41e3238..e46b520 100644
--- a/app/ecs/ecs.js
+++ b/app/ecs/ecs.js
@@ -23,18 +23,22 @@ export default class Ecs {
 
   deferredChanges = {}
 
+  $$deindexing = new Set();
+
   $$destructionDependencies = new Map();
 
   $$detached = new Set();
 
   diff = {};
 
-  Systems = {};
-
   $$entities = {};
 
   $$entityFactory = new EntityFactory();
 
+  $$reindexing = new Set();
+
+  Systems = {};
+
   constructor({Systems, Components} = {}) {
     for (const componentName in Components) {
       this.Components[componentName] = new Components[componentName](this);
@@ -129,8 +133,8 @@ export default class Ecs {
   attach(entityIds) {
     for (const entityId of entityIds) {
       this.$$detached.delete(entityId);
+      this.$$reindexing.add(entityId);
     }
-    this.reindex(entityIds);
   }
 
   changed(criteria) {
@@ -209,6 +213,7 @@ export default class Ecs {
         }
       }
       entityIds.add(entityId);
+      this.$$reindexing.add(entityId);
       this.rebuild(entityId, () => componentNames);
       for (const componentName of componentNames) {
         if (!creating[componentName]) {
@@ -234,7 +239,6 @@ export default class Ecs {
         this.markChange(entityId, components);
       }
     }
-    this.reindex(entityIds);
     return entityIds;
   }
 
@@ -301,8 +305,9 @@ export default class Ecs {
 
   destroyMany(entityIds) {
     const destroying = {};
-    this.deindex(entityIds);
+    // this.deindex(entityIds);
     for (const entityId of entityIds) {
+      this.$$deindexing.add(entityId);
       if (!this.$$entities[entityId]) {
         throw new Error(`can't destroy non-existent entity ${entityId}`);
       }
@@ -323,8 +328,8 @@ export default class Ecs {
   }
 
   detach(entityIds) {
-    this.deindex(entityIds);
     for (const entityId of entityIds) {
+      this.$$deindexing.add(entityId);
       this.$$detached.add(entityId);
     }
   }
@@ -358,6 +363,7 @@ export default class Ecs {
         diff[componentName] = {};
         inserting[componentName].push([entityId, components[componentName]]);
       }
+      this.$$reindexing.add(entityId);
       unique.add(entityId);
       this.markChange(entityId, diff);
     }
@@ -366,7 +372,6 @@ export default class Ecs {
       promises.push(this.Components[componentName].insertMany(inserting[componentName]));
     }
     await Promise.all(promises);
-    this.reindex(unique);
   }
 
   markChange(entityId, components) {
@@ -383,13 +388,7 @@ export default class Ecs {
     }
     // Created?
     else if (!this.diff[entityId]) {
-      const filtered = {};
-      for (const componentName in components) {
-        filtered[componentName] = false === components[componentName]
-          ? false
-          : components[componentName];
-      }
-      this.diff[entityId] = filtered;
+      this.diff[entityId] = components;
     }
     // Otherwise, merge.
     else {
@@ -487,6 +486,7 @@ export default class Ecs {
     const removing = {};
     const unique = new Set();
     for (const [entityId, components] of entities) {
+      this.$$reindexing.add(entityId);
       unique.add(entityId);
       const diff = {};
       for (const componentName of components) {
@@ -502,7 +502,6 @@ export default class Ecs {
     for (const componentName in removing) {
       this.Components[componentName].destroyMany(removing[componentName]);
     }
-    this.reindex(unique);
   }
 
   static serialize(ecs, view) {
@@ -523,6 +522,26 @@ export default class Ecs {
   }
 
   tick(elapsed) {
+    // destroy entities
+    const destroying = new Set();
+    for (const [entityId, {promises}] of this.$$destructionDependencies) {
+      if (0 === promises.size) {
+        destroying.add(entityId);
+      }
+    }
+    if (destroying.size > 0) {
+      this.destroyMany(destroying);
+      for (const entityId of destroying) {
+        this.$$destructionDependencies.get(entityId).resolvers.resolve();
+        this.$$destructionDependencies.delete(entityId);
+      }
+    }
+    // update indices
+    this.deindex(this.$$deindexing);
+    this.$$deindexing.clear();
+    this.reindex(this.$$reindexing);
+    this.$$reindexing.clear();
+    // tick systems
     for (const systemName in this.Systems) {
       const System = this.Systems[systemName];
       if (!System.active) {
@@ -538,19 +557,6 @@ export default class Ecs {
         System.elapsed -= System.frequency;
       }
     }
-    const destroying = new Set();
-    for (const [entityId, {promises}] of this.$$destructionDependencies) {
-      if (0 === promises.size) {
-        destroying.add(entityId);
-      }
-    }
-    if (destroying.size > 0) {
-      this.destroyMany(destroying);
-      for (const entityId of destroying) {
-        this.$$destructionDependencies.get(entityId).resolvers.resolve();
-        this.$$destructionDependencies.delete(entityId);
-      }
-    }
   }
 
   toJSON() {
@@ -583,6 +589,7 @@ export default class Ecs {
         }
         updating[componentName].push([entityId, components[componentName]]);
       }
+      this.$$reindexing.add(entityId);
       unique.add(entityId);
     }
     const promises = [];
@@ -590,7 +597,6 @@ export default class Ecs {
       promises.push(this.Components[componentName].updateMany(updating[componentName]));
     }
     await Promise.all(promises);
-    this.reindex(unique);
   }
 
 }
diff --git a/app/ecs/query.js b/app/ecs/query.js
index ec5ed2b..42f3abf 100644
--- a/app/ecs/query.js
+++ b/app/ecs/query.js
@@ -2,7 +2,7 @@ export default class Query {
 
   $$criteria = {with: [], without: []};
   $$ecs;
-  $$index = new Set();
+  $$map = new Map();
 
   constructor(parameters, ecs) {
     this.$$ecs = ecs;
@@ -20,19 +20,19 @@ export default class Query {
   }
 
   get count() {
-    return this.$$index.size;
+    return this.$$map.size;
   }
 
   deindex(entityIds) {
     for (const entityId of entityIds) {
-      this.$$index.delete(entityId);
+      this.$$map.delete(entityId);
     }
   }
 
   reindex(entityIds) {
     if (0 === this.$$criteria.with.length && 0 === this.$$criteria.without.length) {
       for (const entityId of entityIds) {
-        this.$$index.add(entityId);
+        this.$$map.set(entityId, this.$$ecs.get(entityId));
       }
       return;
     }
@@ -53,28 +53,16 @@ export default class Query {
         }
       }
       if (should) {
-        this.$$index.add(entityId);
+        this.$$map.set(entityId, this.$$ecs.get(entityId));
       }
       else if (!should) {
-        this.$$index.delete(entityId);
+        this.$$map.delete(entityId);
       }
     }
   }
 
   select() {
-    const it = this.$$index.values();
-    return {
-      [Symbol.iterator]() {
-        return this;
-      },
-      next: () => {
-        const result = it.next();
-        if (result.done) {
-          return {done: true, value: undefined};
-        }
-        return {done: false, value: this.$$ecs.get(result.value)};
-      },
-    };
+    return this.$$map.values();
   }
 
 }