diff --git a/include/libu64/u64types.h b/include/libu64/u64types.h
index c05977a6..eafc768b 100644
--- a/include/libu64/u64types.h
+++ b/include/libu64/u64types.h
@@ -11,6 +11,10 @@ typedef struct xy_s {
     f32 x, y;
 } xy_t;
 
+typedef struct xz_s {
+    f32 x, z;
+} xz_t;
+
 typedef struct xyz_s {
     f32 x, y, z;
 } xyz_t;
diff --git a/include/m_collision_bg.h b/include/m_collision_bg.h
index af5db379..159045e7 100644
--- a/include/m_collision_bg.h
+++ b/include/m_collision_bg.h
@@ -70,6 +70,28 @@ enum {
   mCoBG_KILL_PLANT = 7 /* No growth, all plants die on this unit  */
 };
 
+enum {
+  mCoBG_DIRECT_N,
+  mCoBG_DIRECT_W,
+  mCoBG_DIRECT_S,
+  mCoBG_DIRECT_E,
+  mCoBG_DIRECT_NW,
+  mCoBG_DIRECT_NE,
+  mCoBG_DIRECT_SE,
+  mCoBG_DIRECT_SW,
+
+  mCoBG_DIRECT_NUM
+};
+
+enum {
+  mCoBG_AREA_N,
+  mCoBG_AREA_W,
+  mCoBG_AREA_S,
+  mCoBG_AREA_E,
+
+  mCoBG_AREA_NUM
+};
+
 /* sizeof(mCoBG_CollisionData_c) == 4*/
 typedef struct collision_bg_data_s {
   /* 1------- -------- -------- -------- */ u32 shape:1; /* collision shape */
@@ -87,6 +109,22 @@ typedef union collision_bg_u {
   u32 raw;
 } mCoBG_Collision_u;
 
+typedef struct collision_unit_info_s {
+  mCoBG_Collision_u* collision;
+  f32 leftUp_offset;
+  f32 leftDown_offset;
+  f32 rightDown_offset;
+  f32 rightUp_offset;
+  f32 base_height;
+  f32 pos_x;
+  f32 pos_z;
+  int ut_x;
+  int ut_z;
+  int shape;
+  u8 attribute;
+  mActor_name_t item;
+} mCoBG_UnitInfo_c;
+
 #define mCoBG_HIT_WALL       (1 << 0) /* in contact with *any* wall        */
 #define mCoBG_HIT_WALL_FRONT (1 << 1) /* in contact with wall to the front */
 #define mCoBG_HIT_WALL_RIGHT (1 << 2) /* in contact with wall to the right */
@@ -158,17 +196,37 @@ typedef struct bg_register_s {
 } mCoBG_bg_regist_c;
 
 typedef struct collision_offset_table_s {
-    u8 unit_attribute;
-    s8 centerRight_offset; 
-    s8 leftUp_offset;
-    s8 leftDown_offset;
-    s8 rightDown_offset;
-    s8 rightUp_offset;
-    s8 slate_switch;
+  u8 unit_attribute;
+  s8 centerRight_offset; 
+  s8 leftUp_offset;
+  s8 leftDown_offset;
+  s8 rightDown_offset;
+  s8 rightUp_offset;
+  s8 shape;
 } mCoBG_OffsetTable_c;
 
+typedef struct collision_actor_info_s {
+  mActor_name_t name_id;
+  u8 _02;
+  u8 on_ground;
+  u8 _04;
+  u8 in_water;
+  u8 _06[2]; // alignment?
+  mCoBG_CheckResult_c* check_res_p;
+  xz_t speed_xz0;
+  xz_t speed_xz1;
+  xyz_t center_pos;
+  xyz_t old_center_pos;
+  xyz_t rev_pos;
+  u8 _40[4];
+  f32 _44;
+  f32 _48;
+  f32 _4C;
+  u8 _50[0x20];
+} mCoBG_ActorInf_c;
+
 extern u32 mCoBG_Wpos2BgAttribute_Original(xyz_t wpos);
-extern u32 mCoBG_Wpos2Attribute(xyz_t wpos, char* is_diggable);
+extern u32 mCoBG_Wpos2Attribute(xyz_t wpos, s8* is_diggable);
 extern int mCoBG_CheckWaterAttribute(u32 attribute);
 extern f32 mCoBG_GetBgY_AngleS_FromWpos(s_xyz* angle_to_ground, xyz_t wpos, f32 offset_y);
 extern f32 mCoBG_GetShadowBgY_AngleS_FromWpos(f32, s_xyz*, xyz_t);
@@ -199,6 +257,7 @@ extern int mCoBG_ExistHeightGap_KeepAndNow_Detail(xyz_t wpos);
 extern int mCoBG_GetHoleNumber(xyz_t wpos);
 extern int mCoBG_Attr2CheckPlaceNpc(u32 attribute);
 extern int mCoBG_ExistHeightGap_KeepAndNow(xyz_t wpos);
+extern void mCoBG_GetNorm_By3Point(xyz_t* norm, xyz_t* p0, xyz_t* p1, xyz_t* p2);
 
 extern void mCoBG_InitMoveBgData();
 extern void mCoBG_InitBlockBgCheckMode();
diff --git a/rel/m_collision_bg.c b/rel/m_collision_bg.c
new file mode 100644
index 00000000..535cb207
--- /dev/null
+++ b/rel/m_collision_bg.c
@@ -0,0 +1,406 @@
+#include "m_collision_bg.h"
+
+#include "m_field_info.h"
+#include "m_name_table.h"
+#include "m_actor.h"
+
+static xyz_t mCoBG_unit_offset[mCoBG_DIRECT_NUM] = {
+  {                  0.0f, 0.0f, -mFI_UNIT_BASE_SIZE_F },
+  { -mFI_UNIT_BASE_SIZE_F, 0.0f,                  0.0f },
+  {                  0.0f, 0.0f,  mFI_UNIT_BASE_SIZE_F },
+  {  mFI_UNIT_BASE_SIZE_F, 0.0f,                  0.0f },
+  { -mFI_UNIT_BASE_SIZE_F, 0.0f, -mFI_UNIT_BASE_SIZE_F },
+  { -mFI_UNIT_BASE_SIZE_F, 0.0f,  mFI_UNIT_BASE_SIZE_F },
+  {  mFI_UNIT_BASE_SIZE_F, 0.0f,  mFI_UNIT_BASE_SIZE_F },
+  {  mFI_UNIT_BASE_SIZE_F, 0.0f, -mFI_UNIT_BASE_SIZE_F }
+};
+
+static void mCoBG_PlussDirectOffset(xyz_t* ofs_wpos, xyz_t wpos, int direct) {
+  
+  if (ofs_wpos != NULL && direct >= 0 && direct < mCoBG_DIRECT_NUM) {
+    ofs_wpos->x = wpos.x + mCoBG_unit_offset[direct].x;
+    ofs_wpos->y = wpos.y + mCoBG_unit_offset[direct].y;
+    ofs_wpos->z = wpos.z + mCoBG_unit_offset[direct].z;
+  }
+}
+
+static void mCoBG_SetXyz_t(xyz_t* pos, f32 x, f32 y, f32 z) {
+  pos->x = x;
+  pos->y = y;
+  pos->z = z;
+}
+
+static void mCoBG_SetXZ(xz_t* xz, f32 x, f32 z) {
+  xz->x = x;
+  xz->z = z;
+}
+
+static void mCoBG_Wpos2Upos(xyz_t* upos, xyz_t wpos, int ut_x, int ut_z) {
+  upos->x = wpos.x - (ut_x * mFI_UT_WORLDSIZE_X_F);
+  upos->z = wpos.z - (ut_z * mFI_UT_WORLDSIZE_Z_F);
+
+  upos->x -= mFI_UT_WORLDSIZE_HALF_X_F;
+  upos->z -= mFI_UT_WORLDSIZE_HALF_Z_F;
+}
+
+static void mCoBG_Unit2UnitInfo_OutOfUnitPos(mCoBG_UnitInfo_c* unit_info, int ut_x, int ut_z) {
+  mActor_name_t* item_p;
+
+  unit_info->ut_x = ut_x;
+  unit_info->ut_z = ut_z;
+  unit_info->collision = mFI_UtNum2UtCol(ut_x, ut_z);
+  unit_info->base_height = mFI_UtNum2BaseHeight(ut_x, ut_z);
+  unit_info->leftUp_offset = unit_info->collision->data.top_left * 10.0f + unit_info->base_height;
+  unit_info->leftDown_offset = unit_info->collision->data.bot_left * 10.0f + unit_info->base_height;
+  unit_info->rightUp_offset = unit_info->collision->data.top_right * 10.0f + unit_info->base_height;
+  unit_info->rightDown_offset = unit_info->collision->data.bot_right * 10.0f + unit_info->base_height;
+  unit_info->shape = unit_info->collision->data.shape;
+  unit_info->attribute = unit_info->collision->data.unit_attribute;
+
+  item_p = mFI_UtNum2UtFG(ut_x, ut_z);
+
+  if (item_p != NULL) {
+    unit_info->item = *item_p;
+  }
+  else {
+    unit_info->item = EMPTY_NO;
+  }
+}
+
+static void mCoBG_Wpos2UnitInfo(mCoBG_UnitInfo_c* unit_info, xyz_t wpos) {
+  xyz_t upos = { 0.0f, 0.0f, 0.0f };
+  int ut_x;
+  int ut_z;
+
+  mFI_Wpos2UtNum(&ut_x, &ut_z, wpos);
+  mCoBG_Unit2UnitInfo_OutOfUnitPos(unit_info, ut_x, ut_z);
+  mCoBG_Wpos2Upos(&upos, wpos, ut_x, ut_z);
+  unit_info->pos_x = upos.x;
+  unit_info->pos_z = upos.z;
+}
+
+
+/*
+Area unit triangle
+
+0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
+1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
+1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 
+1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 
+1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 
+1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 
+1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 
+1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 
+1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 
+1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 
+1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 
+1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 
+1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 
+1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 
+
+Bias towards the top and left triangles.
+Top:    440
+Left:   419
+Bottom: 361
+Right:  380
+
+NOTE: The top of the triangle is denoted as the "bottom" by the devs as it is in the -Z direction.
+*/
+
+/* This function works on a "unit position" which is [-20.0f, 20.0f) in XZ */
+static void mCoBG_GetUnitArea(mCoBG_UnitInfo_c* unit_info, s16* unit_area) {
+  f32 x = unit_info->pos_x;
+  f32 z = unit_info->pos_z;
+
+  // Determine the triangle based on the x and z coordinates
+  if (x < z) {
+    if (z > -x) {
+      unit_area[0] = mCoBG_AREA_S;
+    }
+    else {
+      unit_area[0] = mCoBG_AREA_W;
+    }
+  }
+  else if (z > -x) {
+    unit_area[0] = mCoBG_AREA_E;
+  }
+  else { // z <= x && z <= -x
+    unit_area[0] = mCoBG_AREA_N;
+  }
+}
+
+
+static void mCoBG_GetGroundAngleFromVtx3(s_xyz* ground_angle, xyz_t* v0, xyz_t* v1, xyz_t* v2, s16 unit_area) {
+  if (ground_angle != NULL) {
+    xyz_t avg;
+    f32 a0;
+    f32 a1;
+    
+    ground_angle->y = 0;
+    avg.x = 0.5f * (v1->x + v2->x);
+    avg.y = 0.5f * (v1->y + v2->y);
+    avg.z = 0.5f * (v1->z + v2->z);
+
+    switch (unit_area) {
+      case mCoBG_AREA_N:
+      {
+        a0 = v0->z - avg.z;
+        a1 = v0->y - avg.y;
+        ground_angle->x = atans_table(a0, -a1);
+
+        a0 = v1->x - v2->x;
+        a1 = v1->y - v2->y;
+        ground_angle->z = atans_table(a0, a1);
+        break;
+      }
+
+      case mCoBG_AREA_S:
+      {
+        a0 = avg.z - v0->z;
+        a1 = -(avg.y - v0->y);
+        ground_angle->x = atans_table(a0, a1);
+
+        a0 = v2->x - v1->x;
+        a1 = v2->y - v1->y;
+        ground_angle->z = atans_table(a0, a1);
+        break;
+      }
+
+      case mCoBG_AREA_W:
+      {
+        a0 = v2->z - v1->z;
+        a1 = v2->y - v1->y;
+        ground_angle->x = atans_table(a0, -a1);
+        
+        a0 = v0->x - avg.x;
+        a1 = v0->y - avg.y;
+        ground_angle->z = atans_table(a0, a1);
+        break;
+      }
+
+      case mCoBG_AREA_E:
+      {
+        a0 = v1->z - v2->z;
+        a1 = -(v1->y - v2->y);
+        ground_angle->x = atans_table(a0, a1);
+
+        a0 = avg.x - v0->x;
+        a1 = avg.y - v0->y;
+        ground_angle->z = atans_table(a0, a1);
+        break;
+      }
+    }
+  }
+}
+
+static void mCoBG_GetArea3Point(s16 area, xyz_t* v0, xyz_t* v1, xyz_t* v2, mCoBG_Collision_u* col) {
+  switch (area) {
+    case mCoBG_AREA_N:
+    {
+      v0->y = col->data.center * 10.0f;
+      v1->x = mFI_UT_WORLDSIZE_HALF_X_F;
+      v1->y = col->data.bot_right * 10.0f;
+      v1->z = -mFI_UT_WORLDSIZE_HALF_Z_F;
+      v2->x = -mFI_UT_WORLDSIZE_HALF_X_F;
+      v2->y = col->data.top_left * 10.0f; /* BUG? Shouldn't this be bot_left (top = +Z, bot = -Z) of the triangle */
+      v2->z = -mFI_UT_WORLDSIZE_HALF_Z_F;
+      break;
+    }
+
+    case mCoBG_AREA_W:
+    {
+      v0->y = col->data.center * 10.0f;
+      v1->x = -mFI_UT_WORLDSIZE_HALF_X_F;
+      v1->y = col->data.top_left * 10.0f;
+      v1->z = -mFI_UT_WORLDSIZE_HALF_Z_F;
+      v2->x = -mFI_UT_WORLDSIZE_HALF_X_F;
+      v2->y = col->data.bot_left * 10.0f;
+      v2->z = mFI_UT_WORLDSIZE_HALF_Z_F;
+      break;
+    }
+
+    case mCoBG_AREA_S:
+    {
+      v0->y = col->data.center * 10.0f;
+      v1->x = -mFI_UT_WORLDSIZE_HALF_X_F;
+      v1->y = col->data.bot_left * 10.0f;  /* BUG? Shouldn't this be top_left (top = +Z, bot = -Z) of the triangle */
+      v1->z = mFI_UT_WORLDSIZE_HALF_Z_F;
+      v2->x = mFI_UT_WORLDSIZE_HALF_X_F;
+      v2->y = col->data.top_right * 10.0f;
+      v2->z = mFI_UT_WORLDSIZE_HALF_Z_F;
+      break;
+    }
+
+    case mCoBG_AREA_E:
+    {
+      v0->y = col->data.center * 10.0f;
+      v1->x = mFI_UT_WORLDSIZE_HALF_X_F;
+      v1->y = col->data.top_right * 10.0f;
+      v1->z = mFI_UT_WORLDSIZE_HALF_Z_F;
+      v2->x = mFI_UT_WORLDSIZE_HALF_X_F;
+      v2->y = col->data.bot_right * 10.0f;
+      v2->z = -mFI_UT_WORLDSIZE_HALF_Z_F;
+      break;
+    }
+  }
+}
+
+static void mCoBG_GetNormTriangle(xyz_t* norm, s_xyz* ground_angle, mCoBG_Collision_u* col, s16 area) {
+  xyz_t v0 = { 0.0f, 0.0f, 0.0f };
+  xyz_t v1 = { 0.0f, 0.0f, 0.0f };
+  xyz_t v2 = { 0.0f, 0.0f, 0.0f };
+
+  mCoBG_GetArea3Point(area, &v0, &v1, &v2, col);
+  mCoBG_GetNorm_By3Point(norm, &v0, &v1, &v2);
+  mCoBG_GetGroundAngleFromVtx3(ground_angle, &v0, &v1, &v2, area);
+}
+
+static mCoBG_ActorInf_c l_ActorInf;
+
+static void mCoBG_AdjustActorY(xyz_t* rev_pos, ACTOR* actor, f32 ground_y, f32 water_y, f32 ground_dist, mCoBG_CheckResult_c* check_res, mCoBG_ActorInf_c* actor_info, int check_water) {
+  actor->bg_collision_check.ground_y = ground_y;
+
+  if (check_water) {
+    f32 actor_y = actor->world.position.y;
+    f32 actor_foot_y = actor_y + ground_dist;
+    f32 water_ground_y = (water_y - (mFI_UNIT_BASE_SIZE_F / 2.0f));
+
+    if (water_ground_y >= actor_foot_y) {
+      rev_pos->y = (water_ground_y - ground_dist) - actor_y;
+      check_res->is_in_water = TRUE;
+      check_res->on_ground = TRUE;
+      actor->position_speed.y = 0.0f;
+    }
+    else if (water_y >= actor_foot_y) {
+      check_res->is_in_water = TRUE;
+    }
+  }
+  else {
+    f32 actor_y = actor->world.position.y;
+    f32 actor_foot_y = actor_y + ground_dist;
+
+    if (ground_y >= actor_foot_y) {
+      rev_pos->y = (ground_y - ground_dist) - actor_y;
+      check_res->on_ground = TRUE;
+      actor->position_speed.y = 0.0f; // stop actor from moving downward anymore
+    }
+    else if (actor_info->on_ground && actor_info->_48 > actor_info->_4C) {
+      f32 dist_to_ground = ABS(ground_y - actor_foot_y);
+      f32 xz_vel = sqrtf(actor_info->speed_xz0.x * actor_info->speed_xz0.x + actor_info->speed_xz0.z * actor_info->speed_xz0.z);
+
+      if (dist_to_ground <= xz_vel) {
+        rev_pos->y = (ground_y - ground_dist) - actor->world.position.y;
+        check_res->on_ground = TRUE;
+        actor->position_speed.y = 0.0f;
+      }
+    }
+  }
+}
+
+static f32 mCoBG_GroundPolygonInfo2BgHeight(xyz_t* norm, mCoBG_UnitInfo_c* unit_info) {
+  f32 dot = -(norm->y * (unit_info->collision->data.center * 10.0f)) + (norm->x * unit_info->pos_x + norm->z * unit_info->pos_z);
+  return dot / -norm->y; // dot product scaled by y normal
+}
+
+static void mCoBG_GetSpeedByWpos(xz_t* speed, ACTOR* actor) {
+  speed->x = actor->world.position.x - actor->last_world_position.x;
+  speed->z = actor->world.position.z - actor->last_world_position.z;
+}
+
+static void mCoBG_CarryOutReverse(ACTOR* actor, xyz_t rev_pos, s16 type) {
+  if (type == 0) {
+    actor->world.position.x += rev_pos.x;
+    actor->world.position.y += rev_pos.y;
+    actor->world.position.z += rev_pos.z;
+  }
+
+  if (actor->bg_collision_check.result.unit_attribute >= mCoBG_ATTRIBUTE_WATER && actor->bg_collision_check.result.unit_attribute <= mCoBG_ATTRIBUTE_RIVER_NE) {
+    xyz_t pos = actor->world.position;
+
+    f32 water_height = mCoBG_GetWaterHeight_File(pos, __FILE__, 1303);
+    if ((pos.y + l_ActorInf._44) <= water_height) {
+      actor->bg_collision_check.result.is_in_water = TRUE;
+    }
+  }
+}
+
+static void mCoBG_InitRevpos(xyz_t* rev_pos) {
+  rev_pos->x = 0.0f;
+  rev_pos->y = 0.0f;
+  rev_pos->z = 0.0f;
+}
+
+static void mCoBG_MakeSizeUnitInfo(mCoBG_UnitInfo_c *unit_info, int ut_x, int ut_z, s16 size) {
+  int x;
+  int z;
+  int start_x;
+  int start_z;
+  int end_x;
+  int end_z;
+  
+  start_z = ut_z - (size >> 1);
+  start_x = ut_x - (size >> 1);
+  end_z = start_z + size;
+  end_x = start_x + size;
+
+  for (z = start_z; z < end_z; z++) {
+    for (x = start_x; x < end_x; x++) {
+      mCoBG_Unit2UnitInfo_OutOfUnitPos(unit_info, x, z);
+      unit_info++;
+    }
+  }
+}
+
+
+static void mCoBG_MakeTab2MoveTail(xz_t* dst_xz, xz_t* src_xz) {
+  f32 x_bias = ABS(src_xz->x) / (ABS(src_xz->x) + ABS(src_xz->z));
+  f32 z_bias = 1.0f - x_bias;
+
+  if (src_xz->x > 0.0f) {
+    dst_xz->x -= x_bias * 0.2f;
+  }
+  else if (src_xz->x < 0.0f) {
+    dst_xz->x += x_bias * 0.2f;
+  }
+
+  if (src_xz->z > 0.0f) {
+    dst_xz->z -= z_bias * 0.2f;
+  }
+  else if (src_xz->z < 0.0f) {
+    dst_xz->z += z_bias * 0.2f;
+  }
+}
+
+static void mCoBG_SearchAttribute(xyz_t wpos, int direct, s8* can_dig) {
+  xyz_t next_ut;
+
+  wpos.y = 0.0f;
+  mCoBG_PlussDirectOffset(&next_ut, wpos, direct);
+  mCoBG_Wpos2Attribute(next_ut, can_dig);
+}