diff --git a/cm_changelog.txt b/cm_changelog.txt
index f1e2e2d9e6..53748b67d0 100644
--- a/cm_changelog.txt
+++ b/cm_changelog.txt
@@ -74,6 +74,12 @@ This is usable for any OpenTTD servers
 
 == CHANGELOG ==
 
+*** 12.0 (?? Oct 2021) ***
+- Automatically search servers when opening multiplayer window.
+- Added TeamGame server filtering button.
+- Show town population instead of name in IMBA minimap mode.
+- In polyrail mode placing rail while holding Fn modifier will automatically flatten the land for it.
+
 *** 12.0-RC1 (5 Oct 2021) ***
 - Added experimental rail copy-paste tool.
 - Added client list overlay (toggleable with a button in the regular client list window title).
diff --git a/src/rail_gui.cpp b/src/rail_gui.cpp
index c24f9e0a40..22240a67fc 100644
--- a/src/rail_gui.cpp
+++ b/src/rail_gui.cpp
@@ -399,6 +399,93 @@ static CommandContainer DoRailroadTrackCmd(TileIndex start_tile, TileIndex end_t
 	return ret;
 }
 
+namespace citymania {
+
+static void DoAutodirTerraform(bool diagonal, TileIndex s1, TileIndex e1, TileIndex s2, TileIndex e2) {
+	auto h1 = TileHeight(s1);
+	auto h2 = TileHeight(s2);
+	int diag_flag = (int)diagonal;
+	DoCommandP(e1, s1, ((h1 < h2 ? LM_RAISE : LM_LEVEL) << 1) | diag_flag, CMD_LEVEL_LAND, CcTerraform);
+	DoCommandP(e2, s2, ((h2 < h1 ? LM_RAISE : LM_LEVEL) << 1) | diag_flag, CMD_LEVEL_LAND, CcTerraform);
+}
+
+static void HandleAutodirTerraform(TileIndex start_tile, TileIndex end_tile) {
+	bool eq = (TileX(end_tile) - TileY(end_tile) == TileX(start_tile) - TileY(start_tile));
+	bool ez = (TileX(end_tile) + TileY(end_tile) == TileX(start_tile) + TileY(start_tile));
+	switch (_thd.cm_poly_dir) {
+		case TRACKDIR_X_NE:
+			DoAutodirTerraform(false,
+				TILE_ADDXY(start_tile, 1, 0), end_tile,
+				TILE_ADDXY(start_tile, 1, 1), TILE_ADDXY(end_tile, 0, 1));
+			break;
+		case TRACKDIR_X_SW:
+			DoAutodirTerraform(false,
+				start_tile, TILE_ADDXY(end_tile, 1, 0),
+				TILE_ADDXY(start_tile, 0, 1), TILE_ADDXY(end_tile, 1, 1));
+			break;
+		case TRACKDIR_Y_SE:
+			DoAutodirTerraform(false,
+				start_tile, TILE_ADDXY(end_tile, 0, 1),
+				TILE_ADDXY(start_tile, 1, 0), TILE_ADDXY(end_tile, 1, 1));
+			break;
+		case TRACKDIR_Y_NW:
+			DoAutodirTerraform(false,
+				TILE_ADDXY(start_tile, 0, 1), end_tile,
+				TILE_ADDXY(start_tile, 1, 1), TILE_ADDXY(end_tile, 1, 0));
+			break;
+		case TRACKDIR_LEFT_N: {
+			DoAutodirTerraform(true,
+				TILE_ADDXY(start_tile, 1, 0), TILE_ADDXY(end_tile, eq, 0),
+				TILE_ADDXY(start_tile, 1, 1), TILE_ADDXY(end_tile, 0, !eq));
+			break;
+		}
+		case TRACKDIR_RIGHT_N: {
+			DoAutodirTerraform(true,
+				TILE_ADDXY(start_tile, 0, 1), TILE_ADDXY(end_tile, 0, eq),
+				TILE_ADDXY(start_tile, 1, 1), TILE_ADDXY(end_tile, !eq, 0));
+			break;
+		}
+		case TRACKDIR_LEFT_S: {
+			DoAutodirTerraform(true,
+				TILE_ADDXY(start_tile, 1, 0), TILE_ADDXY(end_tile, 1, !eq),
+				start_tile, TILE_ADDXY(end_tile, eq, 1));
+			break;
+		}
+		case TRACKDIR_RIGHT_S: {
+			DoAutodirTerraform(true,
+				TILE_ADDXY(start_tile, 0, 1), TILE_ADDXY(end_tile, !eq, 1),
+				start_tile, TILE_ADDXY(end_tile, 1, eq));
+			break;
+		}
+		case TRACKDIR_UPPER_E: {
+			DoAutodirTerraform(true,
+				start_tile, TILE_ADDXY(end_tile, 0, !ez),
+				TILE_ADDXY(start_tile, 1, 0), TILE_ADDXY(end_tile, !ez, 1));
+			break;
+		}
+		case TRACKDIR_LOWER_E: {
+			DoAutodirTerraform(true,
+				TILE_ADDXY(start_tile, 1, 1), TILE_ADDXY(end_tile, ez, 1),
+				TILE_ADDXY(start_tile, 1, 0), TILE_ADDXY(end_tile, 0, ez));
+			break;
+		}
+		case TRACKDIR_UPPER_W: {
+			DoAutodirTerraform(true,
+				start_tile, TILE_ADDXY(end_tile, !ez, 0),
+				TILE_ADDXY(start_tile, 0, 1), TILE_ADDXY(end_tile, 1, !ez));
+			break;
+		}
+		case TRACKDIR_LOWER_W: {
+			DoAutodirTerraform(true,
+				TILE_ADDXY(start_tile, 1, 1), TILE_ADDXY(end_tile, 1, ez),
+				TILE_ADDXY(start_tile, 0, 1), TILE_ADDXY(end_tile, ez, 0));
+			break;
+		}
+	}
+}
+
+}  // namespace citymania
+
 static void HandleAutodirPlacement()
 {
 	Track track = (Track)(_thd.drawstyle & HT_DIR_MASK); // 0..5
@@ -416,6 +503,7 @@ static void HandleAutodirPlacement()
 	if (citymania::_estimate_mod || !(_thd.place_mode & HT_POLY) ||
 			DoCommand(&cmd, DC_AUTO | DC_NO_WATER).GetErrorMessage() != STR_ERROR_ALREADY_BUILT ||
 			_rail_track_endtile == INVALID_TILE) {
+		if (_thd.cm_poly_terra) citymania::HandleAutodirTerraform(start_tile, end_tile);
 		/* Execute. */
 		if (!DoCommandP(&cmd)) return;
 	}
@@ -976,6 +1064,14 @@ struct BuildRailToolbarWindow : Window {
 		return ES_NOT_HANDLED;
 	}
 
+	EventState CM_OnFnModStateChange() override
+	{
+		if (this->IsWidgetLowered(WID_RAT_POLYRAIL)) {
+			return ES_HANDLED;
+		}
+		return ES_NOT_HANDLED;
+	}
+
 	static HotkeyList hotkeys;
 };
 
diff --git a/src/tilehighlight_type.h b/src/tilehighlight_type.h
index 717342857f..434262e5ee 100644
--- a/src/tilehighlight_type.h
+++ b/src/tilehighlight_type.h
@@ -91,6 +91,9 @@ struct TileHighlightData {
 
 	citymania::ObjectHighlight cm;
 	citymania::ObjectHighlight cm_new;
+	bool cm_poly_terra;
+	bool cm_new_poly_terra;
+	Trackdir cm_poly_dir;
 
 	void Reset();
 
diff --git a/src/viewport.cpp b/src/viewport.cpp
index 7f675d217e..a326ae3de2 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -1181,7 +1181,7 @@ static void DrawTileSelection(const TileInfo *ti)
 		case HT_LINE: {
 			HighLightStyle type = GetPartOfAutoLine(ti->x, ti->y, _thd.selstart, _thd.selend, _thd.drawstyle & HT_DIR_MASK);
 			if (type < HT_DIR_END) {
-				DrawAutorailSelection(ti, type);
+				DrawAutorailSelection(ti, type, _thd.cm_poly_terra ? CM_SPR_PALETTE_ZONING_YELLOW : PAL_NONE);
 			} else if (_thd.dir2 < HT_DIR_END) {
 				type = GetPartOfAutoLine(ti->x, ti->y, _thd.selstart2, _thd.selend2, _thd.dir2);
 				if (type < HT_DIR_END) DrawAutorailSelection(ti, type, PALETTE_SEL_TILE_BLUE);
@@ -2695,6 +2695,7 @@ void UpdateTileSelection()
 								_thd.new_size.y = y2 - y1 + TILE_SIZE;
 							}
 						}
+						_thd.cm_new_poly_terra = citymania::_fn_mod;
 						break;
 					}
 					/* HT_RAIL */
@@ -2744,6 +2745,7 @@ void UpdateTileSelection()
 			_thd.offs.x != _thd.new_offs.x || _thd.offs.y != _thd.new_offs.y ||
 			_thd.outersize.x != _thd.new_outersize.x ||
 			_thd.outersize.y != _thd.new_outersize.y ||
+			_thd.cm_poly_terra != _thd.cm_new_poly_terra ||
 			_thd.diagonal    != new_diagonal) {
 		/* Clear the old tile selection? */
 		if ((_thd.drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();
@@ -2753,6 +2755,7 @@ void UpdateTileSelection()
 		_thd.size = _thd.new_size;
 		_thd.offs = _thd.new_offs;
 		_thd.outersize = _thd.new_outersize;
+		_thd.cm_poly_terra = _thd.cm_new_poly_terra;
 		_thd.diagonal = new_diagonal;
 		_thd.dirty = 0xff;
 
@@ -3519,6 +3522,7 @@ static HighLightStyle CalcPolyrailDrawstyle(Point pt, bool dragging)
 	_thd.selend.x    -= first_dir.x;
 	_thd.selend.y    -= first_dir.y;
 	Trackdir seldir = PointDirToTrackdir(_thd.selstart, line.first_dir);
+	_thd.cm_poly_dir = seldir;
 	_thd.selstart.x  &= ~TILE_UNIT_MASK;
 	_thd.selstart.y  &= ~TILE_UNIT_MASK;