diff --git a/fcore/bin-search.sml b/fcore/bin-search.sml
index c752672..5f2aee5 100644
--- a/fcore/bin-search.sml
+++ b/fcore/bin-search.sml
@@ -1,23 +1,40 @@
 structure BinSearch =
 struct
-  local
-    fun helpFind (findNum, vec, low, high) =
-      if high >= low then
-        let
-          val mid = low + ((high - low) div 2)
-          val curNum = Vector.sub (vec, mid)
-        in
-          if curNum = findNum then
-            mid
-          else if curNum < findNum then
-            helpFind (findNum, vec, mid + 1, high)
-          else
-            helpFind (findNum, vec, low, mid - 1)
-        end
-      else
-        ~1
-  in
-    fun find (findNum, vec) =
-      helpFind (findNum, vec, 0, Vector.length vec - 1)
-  end
+  fun helpExists (findNum, vec, low, high) =
+    if high >= low then
+      let
+        val mid = low + ((high - low) div 2)
+        val curNum = Vector.sub (vec, mid)
+      in
+        if curNum = findNum then
+          true
+        else if curNum < findNum then
+          helpExists (findNum, vec, mid + 1, high)
+        else
+          helpExists (findNum, vec, low, mid - 1)
+      end
+    else
+      false
+
+  fun exists (findNum, vec) =
+    helpExists (findNum, vec, 0, Vector.length vec - 1)
+
+  fun helpFind (findNum, vec, low, high) =
+    if high >= low then
+      let
+        val mid = low + ((high - low) div 2)
+        val curNum = Vector.sub (vec, mid)
+      in
+        if curNum = findNum then
+          mid
+        else if curNum < findNum then
+          helpFind (findNum, vec, mid + 1, high)
+        else
+          helpFind (findNum, vec, low, mid - 1)
+      end
+    else
+      ~1
+
+  fun find (findNum, vec) =
+    helpFind (findNum, vec, 0, Vector.length vec - 1)
 end
diff --git a/fcore/game-update.sml b/fcore/game-update.sml
index 1f7309d..8601c81 100644
--- a/fcore/game-update.sml
+++ b/fcore/game-update.sml
@@ -47,14 +47,21 @@ struct
         end
     | [] => acc
 
-  fun checkEnemiesWhileAttacking (player, enemies, lst, acc) =
-    let
-      open QuadTree
-    in
-      case lst of
-        enemyID :: tl => (* placeholder *) acc
-      | [] => acc
-    end
+  (* removes enemies from `enemies` vector when that enemy is in collisions *)
+  fun filterEnemyCollisions (pos, collisions, enemies: enemy vector, acc) =
+    if pos < 0 then
+      Vector.fromList acc
+    else
+      let
+        val enemy = Vector.sub (enemies, pos)
+      in
+        if BinSearch.exists (#id enemy, collisions) then
+          (* filter out *)
+          filterEnemyCollisions (pos - 1, collisions, enemies, acc)
+        else
+          (* don't filter out *)
+          filterEnemyCollisions (pos - 1, collisions, enemies, enemy :: acc)
+      end
 
   fun checkPlayerEnemyCollisions (player, game) =
     let
@@ -108,6 +115,10 @@ struct
             val patches =
               checkEnemiesWhileAttacking (player, enemies, enemyCollisions, [])
             val player = Player.withPatches (player, patches)
+
+            val enemyCollisions = Vector.fromList enemyCollisions
+            val enemies = filterEnemyCollisions
+              (Vector.length enemies - 1, enemyCollisions, enemies, [])
           in
             (player, enemies)
           end
@@ -122,6 +133,9 @@ struct
 
       (* check player-enemy collisions and react *)
       val (player, enemies) = checkPlayerEnemyCollisions (player, game)
+
+      (* create enemy quad tree from list of new enemies *)
+      val enemyTree = Enemy.generateTree enemies
     in
       { player = player
       , walls = walls