diff --git a/src/collision.s b/src/collision.s
index eeea510..7aa4179 100644
--- a/src/collision.s
+++ b/src/collision.s
@@ -2,8 +2,12 @@ INCLUDE "oam.inc"
 
 SECTION "Collision", ROM0
 
+DEF COLLF_WALK EQU (1 << 0)
+DEF COLLF_LADDER EQU (1 << 1)
+DEF COLLF_PORTAL EQU (1 << 2)
+
 ; Determines if player has hit the background
-; @return NZ = true, Z = false
+; @return NZ = false, Z = true
 player_bg_collides::
     ; C = MAP X = PLAYER X / 8 + CAMERA X
     ld a, [PLAYER_X]
@@ -15,16 +19,16 @@ player_bg_collides::
     ld c, a
 
     ; C < 0
-    bit 7, c
-    ret nz
+    ld a, c
+    cpl
+    bit 7, a
+    ret z
 
     ; C >= MAP WIDTH
     ld a, [CURRENT_MAP_WIDTH]
     cp c
     jr nz, .load_y
 
-    ; Set NZ
-    or $ff
     ret
 
 .load_y:
@@ -38,8 +42,10 @@ player_bg_collides::
     ld b, a
 
     ; B < 0
-    bit 7, b
-    ret nz
+    ld a, b
+    cpl
+    bit 7, a
+    ret z
 
     ; B >= MAP HEIGHT
     ld a, [CURRENT_MAP_HEIGHT]
@@ -53,18 +59,18 @@ player_bg_collides::
 .check_tiles:
     ; top left
     call can_move_to
-    ret nz
+    ret z
 
     ; top right
     inc c
     call can_move_to
-    ret nz
+    ret z
 
     ; bottom left
     dec c
     inc b
     call can_move_to
-    ret nz
+    ret z
 
     ; bottom right
     inc c
@@ -73,7 +79,7 @@ player_bg_collides::
     ret
 
 ; Check if the player is in mid-air
-; @note NZ = false, Z = true
+; @note NZ = true, Z = false
 player_in_air::
     ; c = x % 8 == 0 ? x/8 : x/8 + 1
     ld a, [PLAYER_X]
@@ -97,7 +103,7 @@ player_in_air::
     inc b
 
     call can_move_to
-    ret nz
+    ret z
 
     inc c
     call can_move_to
@@ -108,7 +114,7 @@ player_in_air::
 ; @param b y-coordinate
 ; @param c x-coordinate
 ; @destroy a, d, e
-; @note NZ = false, Z = true
+; @note NZ = true, Z = false
 can_move_to:
     push bc
     push hl
@@ -129,9 +135,8 @@ can_move_to:
     jr nz, .mul_y_width
     add hl, bc
 
-    ; check [hl] = 1
     ld a, [hl]
-    cp 1
+    and COLLF_WALK
 
     pop hl
     pop bc
diff --git a/src/player.s b/src/player.s
index 839e913..390325a 100644
--- a/src/player.s
+++ b/src/player.s
@@ -13,7 +13,7 @@ PLAYER_DIR:: db
 
 PLAYER_STATE:: db
 PLAYER_VY:: dw
-PLAYER_INV:: DS (2 * PLAYER_INV_SIZE)
+PLAYER_INV:: ds (2 * PLAYER_INV_SIZE)
 
 Section "Player Code", ROM0
 
@@ -62,7 +62,7 @@ Player_Update::
 
     ; initialize jump state if not already jumping
     ld a, [PLAYER_STATE]
-    cp PLAYER_STATEF_JUMP
+    and PLAYER_STATEF_JUMP
     jr nz, .jump_update
 
     ld a, PLAYER_STATEF_JUMP
@@ -74,7 +74,7 @@ Player_Update::
 ; todo: deduplicate
 .jump_update_check:
     ld a, [PLAYER_STATE]
-    cp PLAYER_STATEF_JUMP
+    and PLAYER_STATEF_JUMP
     jr z, .right
 
 .jump_update:
@@ -92,17 +92,17 @@ Player_Update::
     sbc HIGH(GRAVITY)
     ld b, a
 
-    ; we only need to clamp when moving down
-    bit 7, b
-    jr z, .no_clamp
+    ; ; we only need to clamp when moving down
+    ; bit 7, b
+    ; jr z, .no_clamp
 
-    ; vy = MIN(MAX_VY, vy)
-    ld a, b
-    cp HIGH(MAX_VY)
-    jr c, .no_clamp
+    ; ; vy = MIN(MAX_VY, vy)
+    ; ld a, b
+    ; cp HIGH(MAX_VY)
+    ; jr c, .no_clamp
 
-    ld b, HIGH(MAX_VY)
-    ld c, LOW(MAX_VY)
+    ; ld b, HIGH(MAX_VY)
+    ; ld c, LOW(MAX_VY)
 
 .no_clamp:
     ld hl, PLAYER_VY
@@ -119,7 +119,7 @@ Player_Update::
 
     ; roll back jump if there was a collision
     call player_bg_collides
-    jr nz, .jump_rollback
+    jr nz, .jump_Player_UpdateOAM
 
     ; TODO: Enable once scroll zones are implemented
     ; ld a, [PLAYER_VY]
@@ -139,7 +139,7 @@ Player_Update::
 
 .jump_rollback_check:
     call player_bg_collides
-    jr nz, .jump_rollback
+    jr z, .jump_rollback
 
     ; set PLAYER_STATE = PLAYER_STATEF_WALK if VY < 0 (fell into ground)
     ld hl, PLAYER_VY
@@ -177,7 +177,7 @@ Player_Update::
     ld [PLAYER_X], a
 
     call player_bg_collides
-    jr nz, .right_rollback
+    jr z, .right_rollback
 
     ; TODO: Enable once scroll zones are implemented
     ; ld d, PLAYER_SPEED
@@ -211,7 +211,7 @@ Player_Update::
     ld [PLAYER_X], a
 
     call player_bg_collides
-    jr nz, .left_rollback
+    jr z, .left_rollback
 
     ; TODO: Enable once scroll zones are implemented
     ; ld d, PLAYER_SPEED
@@ -230,12 +230,12 @@ Player_Update::
 
 .fall:
     call player_in_air
-    ret nz
+    ret z
 
     ; only set jump state if not already jumping
     ld hl, PLAYER_STATE
     ld a, [hl]
-    or PLAYER_STATEF_JUMP
+    and PLAYER_STATEF_JUMP
     ret nz
 
     ld [hl], PLAYER_STATEF_JUMP