diff --git a/fcore/constants.sml b/fcore/constants.sml
index 795bd6b..e9aef27 100644
--- a/fcore/constants.sml
+++ b/fcore/constants.sml
@@ -30,7 +30,10 @@ struct
   val enemySize = 35
   val enemySizeReal: Real32.real = 35.0
   val moveEnemyBy = 3
+
   val batRestLimit = 55
+  val moveBatX = 1
+  val moveBatY = 2
 
   val moveProjectileBy = 11
 end
diff --git a/fcore/enemy/enemy-behaviour.sml b/fcore/enemy/enemy-behaviour.sml
index 8abeec1..6d67e95 100644
--- a/fcore/enemy/enemy-behaviour.sml
+++ b/fcore/enemy/enemy-behaviour.sml
@@ -502,50 +502,58 @@ struct
   fun updateStraightBat
     (player, enemy, walls, wallTree, projectileTree, enemyList, fallingList) =
     let
-      val {x, y, batRest, ...} = enemy
+      val {x, y, batRest, batDirY, batMinY, batMaxY, xAxis, ...} = enemy
+
       val size = Constants.enemySize
-    in
-      if QuadTree.hasCollisionAt (x, y, size, size, ~1, wallTree) then
-        (* has collision with wall *)
-        let
-          val enemy =
-            if batRest >= Constants.batRestLimit then
-              (* make enemy move in opposite direction *)
-              case #xAxis enemy of
-                MOVE_RIGHT =>
-                  EnemyPatch.withPatches
-                    ( enemy
-                    , [ EnemyPatch.W_X_AXIS MOVE_LEFT
-                      , EnemyPatch.W_X (x - (Constants.moveEnemyBy * 9))
-                      ]
-                    )
-              | MOVE_LEFT =>
-                  EnemyPatch.withPatches
-                    ( enemy
-                    , [ EnemyPatch.W_X_AXIS MOVE_RIGHT
-                      , EnemyPatch.W_X (x + (Constants.moveEnemyBy * 9))
-                      ]
-                    )
-              | _ => enemy
+      val moveByY = Constants.moveBatY
+      val moveByX = Constants.moveBatX
+
+      val patches =
+        (* get apatches for up/down movement *)
+        case batDirY of
+          UP =>
+            if y - moveByY <= batMaxY then
+              [EnemyPatch.W_BAT_DIR_Y DOWN, EnemyPatch.W_Y (y + moveByY)]
             else
-              (* keep resting until we hit rest limit *)
-              EnemyPatch.withPatch (enemy, EnemyPatch.W_BAT_REST (batRest + 1))
-        in
-          (enemy :: enemyList, fallingList)
-        end
-      else
-        (* no collision, so continue moving in direction *)
-        let
-          val patches =
-            case #xAxis enemy of
-              MOVE_RIGHT => [EnemyPatch.W_X (x + Constants.moveEnemyBy)]
-            | MOVE_LEFT => [EnemyPatch.W_X (x - Constants.moveEnemyBy)]
-            | STAY_STILL => []
-          val patches = EnemyPatch.W_BAT_REST 0 :: patches
-          val enemy = EnemyPatch.withPatches (enemy, patches)
-        in
-          (enemy :: enemyList, fallingList)
-        end
+              [EnemyPatch.W_Y (y - moveByY)]
+        | DOWN =>
+            if y + moveByY >= batMinY then
+              [EnemyPatch.W_BAT_DIR_Y UP, EnemyPatch.W_Y (y - moveByY)]
+            else
+              [EnemyPatch.W_Y (y + moveByY)]
+
+      val patches =
+        (* get patches for horizontal movement *)
+        if QuadTree.hasCollisionAt (x, y, size, size, ~1, wallTree) then
+          (* has collision with wall *)
+          if batRest >= Constants.batRestLimit then
+            (* make enemy move in opposite direction *)
+            case xAxis of
+              MOVE_RIGHT =>
+                EnemyPatch.W_X_AXIS MOVE_LEFT :: EnemyPatch.W_X (x - 1)
+                :: patches
+            | MOVE_LEFT =>
+                EnemyPatch.W_X_AXIS MOVE_RIGHT :: EnemyPatch.W_X (x + 1)
+                :: patches
+            | _ => patches
+          else
+            (* keep resting until we hit rest limit *)
+            EnemyPatch.W_BAT_REST (batRest + 1) :: patches
+        else
+          (* no collision, so continue moving in direction *)
+          let
+            val patches =
+              case xAxis of
+                MOVE_RIGHT => EnemyPatch.W_X (x + moveByX) :: patches
+              | MOVE_LEFT => EnemyPatch.W_X (x - moveByX) :: patches
+              | STAY_STILL => patches
+          in
+            EnemyPatch.W_BAT_REST 0 :: patches
+          end
+
+      val enemy = EnemyPatch.withPatches (enemy, patches)
+    in
+      (enemy :: enemyList, fallingList)
     end
 
   fun updateEnemyState
diff --git a/fcore/game-type.sml b/fcore/game-type.sml
index 1ec3bac..8fc6efe 100644
--- a/fcore/game-type.sml
+++ b/fcore/game-type.sml
@@ -234,8 +234,8 @@ struct
         , nextPlatID = ~1
         , batRest = 0
         , batDirY = UP
-        , batMaxY = 635
-        , batMinY = 475
+        , batMaxY = 485
+        , batMinY = 625
         }
       val enemies = Vector.fromList [enemy1]
       val graph = Graph.fromPlatforms (platforms, platformTree)
diff --git a/fcore/quad-tree-fold.sml b/fcore/quad-tree-fold.sml
index e860226..b034167 100644
--- a/fcore/quad-tree-fold.sml
+++ b/fcore/quad-tree-fold.sml
@@ -10,9 +10,15 @@ signature MAKE_QUAD_TREE_FOLD =
 sig
   structure Fn: QUAD_FOLDER
 
-  val foldRegion: int * int * int * int * 
-                  Fn.env * Fn.state * {tree: QuadTreeType.t, width: int, height: int}
-                  -> Fn.state
+  val foldRegion:
+    int
+    * int
+    * int
+    * int
+    * Fn.env
+    * Fn.state
+    * {tree: QuadTreeType.t, width: int, height: int}
+    -> Fn.state
 end
 
 functor MakeQuadTreeFold(Fn: QUAD_FOLDER): MAKE_QUAD_TREE_FOLD =
@@ -50,38 +56,79 @@ struct
 
           val state =
             if vtl then
-              helpFoldRegion 
-                (rx, ry, rw, rh, env, state, qx, qy, hw, hh, Vector.sub (nodes, tlIdx))
+              helpFoldRegion
+                ( rx
+                , ry
+                , rw
+                , rh
+                , env
+                , state
+                , qx
+                , qy
+                , hw
+                , hh
+                , Vector.sub (nodes, tlIdx)
+                )
             else
               state
 
-          val state = 
+          val state =
             if vtr then
-              helpFoldRegion 
-                (rx, ry, rw, rh, env, state, qx + hw, qy, hw, hh, Vector.sub (nodes, trIdx))
-            else 
+              helpFoldRegion
+                ( rx
+                , ry
+                , rw
+                , rh
+                , env
+                , state
+                , qx + hw
+                , qy
+                , hw
+                , hh
+                , Vector.sub (nodes, trIdx)
+                )
+            else
               state
 
-          val state = 
+          val state =
             if vbl then
               helpFoldRegion
-                (rx, ry, rw, rh, env, state, qx, qy + hh, hw, hh, Vector.sub (nodes, blIdx))
+                ( rx
+                , ry
+                , rw
+                , rh
+                , env
+                , state
+                , qx
+                , qy + hh
+                , hw
+                , hh
+                , Vector.sub (nodes, blIdx)
+                )
             else
               state
         in
           if vbr then
-            helpFoldRegion 
-              (rx, ry, rw, rh, env, state, qw + hw, qy + hh, hw, hh, Vector.sub (nodes, brIdx))
+            helpFoldRegion
+              ( rx
+              , ry
+              , rw
+              , rh
+              , env
+              , state
+              , qw + hw
+              , qy + hh
+              , hw
+              , hh
+              , Vector.sub (nodes, brIdx)
+              )
           else
             state
         end
-    | LEAF items =>
-        foldRegionVec (rx, ry, rw, rh, env, state, 0, items)
+    | LEAF items => foldRegionVec (rx, ry, rw, rh, env, state, 0, items)
 
   fun foldRegion (rx, ry, rw, rh, env, state, tree) =
-    let
-      val {width, height, tree} = tree
-    in
-      helpFoldRegion (rx, ry, rw, rh, env, state, 0, 0, width, height, tree)
+    let val {width, height, tree} = tree
+    in helpFoldRegion (rx, ry, rw, rh, env, state, 0, 0, width, height, tree)
     end
 end
diff --git a/fcore/quad-tree-type.sml b/fcore/quad-tree-type.sml
index c931951..7f46775 100644
--- a/fcore/quad-tree-type.sml
+++ b/fcore/quad-tree-type.sml
@@ -2,51 +2,33 @@ signature QUAD_TREE_TYPE =
 sig
   type item = {itemID: int, startX: int, startY: int, width: int, height: int}
 
-  datatype t =
-    NODE of t vector
-  | LEAF of item vector
+  datatype t = NODE of t vector | LEAF of item vector
 
   val tlIdx: int
   val trIdx: int
   val blIdx: int
   val brIdx: int
 
-  val isColliding: int * int * int * int *
-                   int * int * int * int
-                   -> bool
+  val isColliding: int * int * int * int * int * int * int * int -> bool
 
-  val isCollidingPlus: int * int * int * int *
-                       int * int * int * int
-                       -> bool
+  val isCollidingPlus: int * int * int * int * int * int * int * int -> bool
 
-  val isCollidingItem: int * int * int * int * 
-                       int * item 
-                       -> bool
+  val isCollidingItem: int * int * int * int * int * item -> bool
 
-  val visitTopLeft: int * int * int * int *
-                    int * int * int * int
-                    -> bool
+  val visitTopLeft: int * int * int * int * int * int * int * int -> bool
 
-  val visitTopRight: int * int * int * int *
-                     int * int * int * int
-                     -> bool
+  val visitTopRight: int * int * int * int * int * int * int * int -> bool
 
-  val visitBottomLeft: int * int * int * int *
-                       int * int * int * int
-                       -> bool
+  val visitBottomLeft: int * int * int * int * int * int * int * int -> bool
 
-  val visitBottomRight: int * int * int * int *
-                        int * int * int * int
-                        -> bool
+  val visitBottomRight: int * int * int * int * int * int * int * int -> bool
 end
 
 structure QuadTreeType :> QUAD_TREE_TYPE =
 struct
   type item = {itemID: int, startX: int, startY: int, width: int, height: int}
 
-  datatype t =
-    NODE of t vector
-  | LEAF of item vector
+  datatype t = NODE of t vector | LEAF of item vector
 
   val tlIdx = 0
   val trIdx = 1
diff --git a/fcore/quad-tree.sml b/fcore/quad-tree.sml
index 43e3f06..611ae87 100644
--- a/fcore/quad-tree.sml
+++ b/fcore/quad-tree.sml
@@ -26,7 +26,7 @@ struct
       val vec = Vector.fromList []
       val tree = LEAF vec
     in
-      { tree = tree, width = width, height = height }
+      {tree = tree, width = width, height = height}
     end
 
   fun mkItem (id, startX, startY, width, height) : item =
@@ -41,10 +41,8 @@ struct
   val maxSize = 16
 
   fun mkLeaf items =
-    let
-      val items = Vector.fromList items
-    in
-      LEAF items
+    let val items = Vector.fromList items
+    in LEAF items
     end
 
   fun splitLeaf
@@ -65,7 +63,7 @@ struct
         val tr = mkLeaf tr
         val bl = mkLeaf bl
         val br = mkLeaf br
-        val nodes =  Vector.fromList [tl, tr, bl, br]
+        val nodes = Vector.fromList [tl, tr, bl, br]
       in
         NODE nodes
       end
@@ -101,20 +99,18 @@ struct
 
           val tl = Vector.sub (nodes, tlIdx)
           val tl =
-            if vtl then
-              helpInsert (ix, iy, iw, ih, itemID, qw, qy, hw, hh, tl)
-            else 
-              tl
+            if vtl then helpInsert (ix, iy, iw, ih, itemID, qw, qy, hw, hh, tl)
+            else tl
 
           val tr = Vector.sub (nodes, trIdx)
           val tr =
             if vtr then
               helpInsert (ix, iy, iw, ih, itemID, qx + hw, qy, hw, hh, tr)
-            else 
+            else
               tr
 
           val bl = Vector.sub (nodes, blIdx)
-          val bl = 
+          val bl =
             if vbl then
               helpInsert (ix, iy, iw, ih, itemID, qx, qy + hh, hw, hh, bl)
             else
@@ -124,7 +120,7 @@ struct
           val br =
             if vbr then
               helpInsert (ix, iy, iw, ih, itemID, qx + hw, qy + hh, hw, hh, br)
-            else 
+            else
               br
 
           val nodes = Vector.fromList [tl, tr, bl, br]
@@ -160,35 +156,40 @@ struct
   fun insert (iX, iY, iW, iH, itemID, tree: t) =
     let
       val {width, height, tree} = tree
-      val tree =
-        helpInsert (iX, iY, iW, iH, itemID, 0, 0, width, height, tree)
+      val tree = helpInsert (iX, iY, iW, iH, itemID, 0, 0, width, height, tree)
     in
       {width = width, height = height, tree = tree}
     end
 
-  structure GetCollisions = MakeQuadTreeFold (struct
-    type env = unit
-    type state = int list
-    fun fold (itemID, (), lst) = itemID :: lst
-  end)
+  structure GetCollisions =
+    MakeQuadTreeFold
+      (struct
+         type env = unit
+         type state = int list
+         fun fold (itemID, (), lst) = itemID :: lst
+       end)
 
   fun getCollisions (itemX, itemY, itemWidth, itemHeight, _, tree) =
     GetCollisions.foldRegion (itemX, itemY, itemWidth, itemHeight, (), [], tree)
 
-  structure HasCollisionAt = MakeQuadTreeFold (struct
-    type env = unit
-    type state = bool
-    fun fold _ = true
-  end)
+  structure HasCollisionAt =
+    MakeQuadTreeFold
+      (struct
+         type env = unit
+         type state = bool
+         fun fold _ = true
+       end)
 
   fun hasCollisionAt (ix, iy, iw, ih, _, tree) =
     HasCollisionAt.foldRegion (ix, iy, iw, ih, (), false, tree)
 
-  structure GetItemID = MakeQuadTreeFold (struct
-    type env = unit
-    type state = int
-    fun fold (itemID, (), curID) = Int.max (itemID, curID)
-  end)
+  structure GetItemID =
+    MakeQuadTreeFold
+      (struct
+         type env = unit
+         type state = int
+         fun fold (itemID, (), curID) = Int.max (itemID, curID)
+       end)
 
   fun getItemID (ix, iy, iw, ih, tree) =
     GetItemID.foldRegion (ix, iy, iw, ih, (), ~1, tree)