diff --git a/data/dynos_opt_render.cpp b/data/dynos_opt_render.cpp
index d182e5e3..9fd0daa8 100644
--- a/data/dynos_opt_render.cpp
+++ b/data/dynos_opt_render.cpp
@@ -62,7 +62,11 @@ static void PrintString(const Label& aLabel, s32 aX, s32 aY, u32 aFrontColorRGBA
 }
 
 static void PrintBox(s32 aX, s32 aY, s32 aWidth, s32 aHeight, u32 aColorRGBA, bool aAlignLeft) {
+#ifdef COOP
+    if ((aColorRGBA & 0xFF) != 0) {
+#else
     if ((aColorRGBA && 0xFF) != 0) {
+#endif
         Mtx *_Matrix = (Mtx *) alloc_display_list(sizeof(Mtx));
         if (!_Matrix) return;
         if (aAlignLeft) {
diff --git a/src/audio/data.c b/src/audio/data.c
index 57e093f7..7bf9fb8a 100644
--- a/src/audio/data.c
+++ b/src/audio/data.c
@@ -183,8 +183,8 @@ s8 gVibratoCurve[16] = { 0, 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, 104,
 
 struct AdsrEnvelope gDefaultEnvelope[] = {
     { BE_TO_HOST16(4), BE_TO_HOST16(32000) },    // go from 0 to 32000 over the course of 16ms
-    { BE_TO_HOST16(1000), BE_TO_HOST16(32000) }, // stay there for 4.16 seconds
-    { BE_TO_HOST16(ADSR_HANG), 0 }          // then continue staying there
+    { (s16)BE_TO_HOST16(1000), BE_TO_HOST16(32000) }, // stay there for 4.16 seconds
+    { (s16)BE_TO_HOST16(ADSR_HANG), 0 }          // then continue staying there
 };
 #endif
 
diff --git a/src/game/camera.c b/src/game/camera.c
index c9555c94..abdfd0bc 100644
--- a/src/game/camera.c
+++ b/src/game/camera.c
@@ -1714,6 +1714,7 @@ struct ParallelTrackingPoint sBBHLibraryParTrackPath[] = {
 };
 
 s32 unused_update_mode_5_camera(UNUSED struct Camera *c, UNUSED Vec3f focus, UNUSED Vec3f pos) {
+    return 0;
 }
 
 static void stub_camera_1(UNUSED s32 unused) {
@@ -2039,6 +2040,7 @@ void mode_behind_mario_camera(struct Camera *c) {
 }
 
 s32 nop_update_water_camera(UNUSED struct Camera *c, UNUSED Vec3f focus, UNUSED Vec3f pos) {
+    return 0;
 }
 
 /**
@@ -5435,7 +5437,7 @@ void determine_pushing_or_pulling_door(s16 *rotation) {
     if (sMarioCamState->action == ACT_PULLING_DOOR) {
         *rotation = 0;
     } else {
-        *rotation = DEGREES(180);
+        *rotation = (s16)DEGREES(180);
     }
 }
 
@@ -9606,8 +9608,8 @@ s32 intro_peach_move_camera_start_to_pipe(struct Camera *c, struct CutsceneSplin
 
     // The two splines used by this function are reflected in the horizontal plane for some reason,
     // so they are rotated every frame. Why do this, Nintendo?
-    rotate_in_xz(c->focus, c->focus, DEGREES(180));
-    rotate_in_xz(c->pos, c->pos, DEGREES(180));
+    rotate_in_xz(c->focus, c->focus, (s16)DEGREES(180));
+    rotate_in_xz(c->pos, c->pos, (s16)DEGREES(180));
 
     vec3f_set(offset, -1328.f, 260.f, 4664.f);
     vec3f_add(c->focus, offset);
diff --git a/src/game/mario_actions_airborne.c b/src/game/mario_actions_airborne.c
index fa73fd89..0512254a 100644
--- a/src/game/mario_actions_airborne.c
+++ b/src/game/mario_actions_airborne.c
@@ -77,11 +77,11 @@ s32 check_fall_damage(struct MarioState *m, u32 hardFallAction) {
 #pragma GCC diagnostic ignored "-Wtype-limits"
 
     //! Never true
-    if (m->actionState == ACT_GROUND_POUND) {
+    /*if (m->actionState == ACT_GROUND_POUND) {
         damageHeight = 600.0f;
-    } else {
+    } else {*/
         damageHeight = 1150.0f;
-    }
+    //}
 
 #pragma GCC diagnostic pop
 
diff --git a/src/game/object_collision.c b/src/game/object_collision.c
index f899ea08..8384995e 100644
--- a/src/game/object_collision.c
+++ b/src/game/object_collision.c
@@ -108,7 +108,7 @@ s32 detect_object_hitbox_overlap(struct Object *a, struct Object *b) {
         return 1;
     }
 
-    //! no return value
+    return 0;
 }
 
 s32 detect_object_hurtbox_overlap(struct Object *a, struct Object *b) {
@@ -140,7 +140,7 @@ s32 detect_object_hurtbox_overlap(struct Object *a, struct Object *b) {
         return 1;
     }
 
-    //! no return value
+    return 0;
 }
 
 void clear_object_collision(struct Object *a) {
diff --git a/src/game/paintings.c b/src/game/paintings.c
index 5bfcd56d..95c21012 100644
--- a/src/game/paintings.c
+++ b/src/game/paintings.c
@@ -280,6 +280,7 @@ f32 painting_ripple_y(struct Painting *painting, s8 ySource) {
             return painting->size / 2.0; // some concentric ripples don't care about Mario
             break;
     }
+    return painting->size / 2.0;
 }
 
 /**
@@ -305,6 +306,7 @@ f32 painting_nearest_4th(struct Painting *painting) {
     } else if (painting->floorEntered & ENTER_RIGHT) {
         return thirdQuarter;
     }
+    return thirdQuarter;
 }
 
 /**
@@ -336,6 +338,7 @@ f32 painting_ripple_x(struct Painting *painting, s8 xSource) {
             return painting->size / 2.0;
             break;
     }
+    return painting->size / 2.0;
 }
 
 /**
diff --git a/src/game/screen_transition.c b/src/game/screen_transition.c
index ab36bbc6..45870cd5 100644
--- a/src/game/screen_transition.c
+++ b/src/game/screen_transition.c
@@ -324,6 +324,7 @@ s32 render_screen_transition(s8 fadeTimer, s8 transType, u8 transTime, struct Wa
             return render_textured_transition(fadeTimer, transTime, transData, TEX_TRANS_BOWSER, TRANS_TYPE_MIRROR);
             break;
     }
+    return render_textured_transition(fadeTimer, transTime, transData, TEX_TRANS_BOWSER, TRANS_TYPE_MIRROR);
 }
 
 Gfx *render_cannon_circle_base(void) {
diff --git a/src/game/shadow.c b/src/game/shadow.c
index ec94f909..897c54e6 100644
--- a/src/game/shadow.c
+++ b/src/game/shadow.c
@@ -188,8 +188,7 @@ f32 get_water_level_below_shadow(struct Shadow *s) {
         gShadowAboveWaterOrLava = TRUE;
         return waterLevel;
     }
-    //! @bug Missing return statement. This compiles to return `waterLevel`
-    //! incidentally.
+    return waterLevel;
 }
 
 /**
diff --git a/src/goddard/renderer.c b/src/goddard/renderer.c
index a82f5c07..933095ef 100644
--- a/src/goddard/renderer.c
+++ b/src/goddard/renderer.c
@@ -2845,7 +2845,7 @@ void stub_renderer_6(UNUSED struct GdObj *obj) {
  * @return  an identifier of the menu just defined
  */
 long defpup(UNUSED const char *menufmt, ...) {
-    //! @bug no return; function was stubbed
+    return 0;
 }
 
 /**
diff --git a/src/pc/gfx/gfx_opengl.c b/src/pc/gfx/gfx_opengl.c
index eb9446ad..7ae82942 100644
--- a/src/pc/gfx/gfx_opengl.c
+++ b/src/pc/gfx/gfx_opengl.c
@@ -172,6 +172,7 @@ static const char *shader_item_to_str(uint32_t item, bool with_alpha, bool only_
                 return "texVal1.a";
         }
     }
+    return "unknown";
 }
 
 static void append_formula(char *buf, size_t *len, uint8_t c[2][4], bool do_single, bool do_multiply, bool do_mix, bool with_alpha, bool only_alpha, bool opt_alpha) {
diff --git a/src/pc/lua/utils/smlua_obj_utils.c b/src/pc/lua/utils/smlua_obj_utils.c
index a4237c9b..569022d7 100644
--- a/src/pc/lua/utils/smlua_obj_utils.c
+++ b/src/pc/lua/utils/smlua_obj_utils.c
@@ -76,11 +76,11 @@ static struct Object* spawn_object_internal(enum BehaviorId behaviorId, enum Mod
 }
 
 struct Object* spawn_sync_object(enum BehaviorId behaviorId, enum ModelExtendedId modelId, f32 x, f32 y, f32 z, LuaFunction objSetupFunction) {
-    spawn_object_internal(behaviorId, modelId, x, y, z, objSetupFunction, true);
+    return spawn_object_internal(behaviorId, modelId, x, y, z, objSetupFunction, true);
 }
 
 struct Object* spawn_non_sync_object(enum BehaviorId behaviorId, enum ModelExtendedId modelId, f32 x, f32 y, f32 z, LuaFunction objSetupFunction) {
-    spawn_object_internal(behaviorId, modelId, x, y, z, objSetupFunction, false);
+    return spawn_object_internal(behaviorId, modelId, x, y, z, objSetupFunction, false);
 }
 
 s32 obj_has_behavior_id(struct Object *o, enum BehaviorId behaviorId) {
diff --git a/src/pc/mods/mods_utils.c b/src/pc/mods/mods_utils.c
index ab635f6d..64db187f 100644
--- a/src/pc/mods/mods_utils.c
+++ b/src/pc/mods/mods_utils.c
@@ -246,7 +246,7 @@ bool directory_sanity_check(struct dirent* dir, char* dirPath, char* outPath) {
     if (strchr(dir->d_name, '\\') != NULL) { return false; }
 
     // skip anything that starts with .
-    if (dir->d_name == NULL || dir->d_name[0] == '.') { return false; }
+    if (dir->d_name[0] == '.') { return false; }
 
     // build path
     if (!concat_path(outPath, dirPath, dir->d_name)) {