diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index 2b5340f87..d5a4f62bf 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -13,6 +13,9 @@
 
 #include <algorithm>
 
+//#include <tracy/tracy/Tracy.hpp>
+
+#include "command.h"
 #include "doomdef.h"
 #include "g_game.h"
 #include "r_local.h"
@@ -30,6 +33,7 @@
 extern "C" {
 	#include "qs22j.h"
 }
+extern "C" consvar_t cv_debugfinishline;
 
 seg_t *curline;
 side_t *sidedef;
@@ -418,7 +422,8 @@ boolean R_IsEmptyLine(seg_t *line, sector_t *front, sector_t *back)
 		// Consider colormaps
 		&& back->extra_colormap == front->extra_colormap
 		&& ((!front->ffloors && !back->ffloors)
-		|| Tag_Compare(&front->tags, &back->tags)));
+		|| Tag_Compare(&front->tags, &back->tags))
+		&& (!cv_debugfinishline.value || back->damagetype == front->damagetype));
 }
 
 boolean R_IsDebugLine(seg_t *line)
@@ -1013,6 +1018,11 @@ static void R_Subsector(size_t num)
 		ceilingcolormap = *frontsector->lightlist[light].extra_colormap;
 	}
 
+	auto sector_damage = [](sector_t* s) { return static_cast<sectordamage_t>(s->damagetype); };
+
+	auto floor_damage = [&](sector_t* s) { return s->flags & MSF_FLIPSPECIAL_FLOOR ? sector_damage(s) : SD_NONE; };
+	auto ceiling_damage = [&](sector_t* s) { return s->flags & MSF_FLIPSPECIAL_CEILING ? sector_damage(s) : SD_NONE; };
+
 	sub->sector->extra_colormap = frontsector->extra_colormap;
 
 	if (P_GetSectorFloorZAt(frontsector, viewx, viewy) < viewz
@@ -1025,7 +1035,7 @@ static void R_Subsector(size_t num)
 			floorcolormap, NULL, NULL, frontsector->f_slope,
 			R_NoEncore(frontsector, &levelflats[frontsector->floorpic], false),
 			R_IsRipplePlane(frontsector, NULL, false),
-			false, frontsector
+			false, frontsector, floor_damage(frontsector)
 		);
 	}
 	else
@@ -1041,7 +1051,7 @@ static void R_Subsector(size_t num)
 			ceilingcolormap, NULL, NULL, frontsector->c_slope,
 			R_NoEncore(frontsector, &levelflats[frontsector->ceilingpic], true),
 			R_IsRipplePlane(frontsector, NULL, true),
-			true, frontsector
+			true, frontsector, ceiling_damage(frontsector)
 		);
 	}
 	else
@@ -1055,9 +1065,20 @@ static void R_Subsector(size_t num)
 	{
 		fixed_t heightcheck, planecenterz;
 
+		auto fof_damage = [&](auto& f)
+		{
+			sector_t* s = rover->master->frontsector;
+			return rover->fofflags & FOF_BLOCKPLAYER ? f(s) : sector_damage(s);
+		};
+
+		auto fof_top_damage = [&] { return fof_damage(floor_damage); };
+		auto fof_bottom_damage = [&] { return fof_damage(ceiling_damage); };
+
 		for (rover = frontsector->ffloors; rover && numffloors < MAXFFLOORS; rover = rover->next)
 		{
-			if (!(rover->fofflags & FOF_EXISTS) || !(rover->fofflags & FOF_RENDERPLANES))
+			bool visible = rover->fofflags & FOF_RENDERPLANES;
+
+			if (!(rover->fofflags & FOF_EXISTS) || (!cv_debugfinishline.value && !visible))
 				continue;
 
 			if (frontsector->cullheight)
@@ -1080,6 +1101,14 @@ static void R_Subsector(size_t num)
 				&& ((viewz < heightcheck && (rover->fofflags & FOF_BOTHPLANES || !(rover->fofflags & FOF_INVERTPLANES)))
 				|| (viewz > heightcheck && (rover->fofflags & FOF_BOTHPLANES || rover->fofflags & FOF_INVERTPLANES))))
 			{
+				sectordamage_t damage = fof_bottom_damage();
+
+				if (!damage && !visible)
+				{
+					rover->norender = leveltime; // Tell R_StoreWallRange to skip this
+					continue;
+				}
+
 				light = R_GetPlaneLight(frontsector, planecenterz,
 					viewz < heightcheck);
 
@@ -1089,7 +1118,7 @@ static void R_Subsector(size_t num)
 					*rover->bottomyoffs, *rover->bottomangle, *frontsector->lightlist[light].extra_colormap, rover, NULL, *rover->b_slope,
 					R_NoEncore(rover->master->frontsector, &levelflats[*rover->bottompic], true),
 					R_IsRipplePlane(rover->master->frontsector, rover, true),
-					true, frontsector
+					true, frontsector, damage
 				);
 
 				ffloor[numffloors].slope = *rover->b_slope;
@@ -1115,6 +1144,14 @@ static void R_Subsector(size_t num)
 				&& ((viewz > heightcheck && (rover->fofflags & FOF_BOTHPLANES || !(rover->fofflags & FOF_INVERTPLANES)))
 				|| (viewz < heightcheck && (rover->fofflags & FOF_BOTHPLANES || rover->fofflags & FOF_INVERTPLANES))))
 			{
+				sectordamage_t damage = fof_top_damage();
+
+				if (!damage && !visible)
+				{
+					rover->norender = leveltime; // Tell R_StoreWallRange to skip this
+					continue;
+				}
+
 				light = R_GetPlaneLight(frontsector, planecenterz, viewz < heightcheck);
 
 				ffloor[numffloors].plane = R_FindPlane(
@@ -1123,7 +1160,7 @@ static void R_Subsector(size_t num)
 					*frontsector->lightlist[light].extra_colormap, rover, NULL, *rover->t_slope,
 					R_NoEncore(rover->master->frontsector, &levelflats[*rover->toppic], false),
 					R_IsRipplePlane(rover->master->frontsector, rover, false),
-					false, frontsector
+					false, frontsector, damage
 				);
 
 				ffloor[numffloors].slope = *rover->t_slope;
@@ -1145,6 +1182,10 @@ static void R_Subsector(size_t num)
 		polyobj_t *po = sub->polyList;
 		sector_t *polysec;
 
+		auto poly_damage = [&](auto& f) { return polysec->flags & POF_SOLID ? f(polysec) : sector_damage(polysec); };
+		auto poly_top_damage = [&] { return poly_damage(floor_damage); };
+		auto poly_bottom_damage = [&] { return poly_damage(ceiling_damage); };
+
 		while (po)
 		{
 			if (numffloors >= MAXFFLOORS)
@@ -1173,7 +1214,7 @@ static void R_Subsector(size_t num)
 					NULL, // will ffloors be slopable eventually?
 					R_NoEncore(polysec, &levelflats[polysec->floorpic], false),
 					false, /* TODO: wet polyobjects? */
-					true, frontsector
+					true, frontsector, poly_bottom_damage()
 				);
 
 				ffloor[numffloors].height = polysec->floorheight;
@@ -1202,7 +1243,7 @@ static void R_Subsector(size_t num)
 					NULL, // will ffloors be slopable eventually?
 					R_NoEncore(polysec, &levelflats[polysec->ceilingpic], true),
 					false, /* TODO: wet polyobjects? */
-					false, frontsector
+					false, frontsector, poly_top_damage()
 				);
 
 				ffloor[numffloors].polyobj = po;
diff --git a/src/r_draw.c b/src/r_draw.c
index 63af42fa9..09f28e104 100644
--- a/src/r_draw.c
+++ b/src/r_draw.c
@@ -117,6 +117,7 @@ INT32 ds_y, ds_x1, ds_x2;
 lighttable_t *ds_colormap;
 lighttable_t *ds_fullbright;
 lighttable_t *ds_translation; // Lactozilla: Sprite splat drawer
+lighttable_t *ds_flatlighting;
 
 fixed_t ds_xfrac, ds_yfrac, ds_xstep, ds_ystep;
 INT32 ds_waterofs, ds_bgofs;
diff --git a/src/r_draw.h b/src/r_draw.h
index 4936674e6..b1d312bf8 100644
--- a/src/r_draw.h
+++ b/src/r_draw.h
@@ -67,6 +67,7 @@ extern INT32 ds_y, ds_x1, ds_x2;
 extern lighttable_t *ds_colormap;
 extern lighttable_t *ds_fullbright;
 extern lighttable_t *ds_translation;
+extern lighttable_t *ds_flatlighting;
 
 extern fixed_t ds_xfrac, ds_yfrac, ds_xstep, ds_ystep;
 extern INT32 ds_waterofs, ds_bgofs;
@@ -78,8 +79,6 @@ extern UINT8 *ds_source;
 extern UINT8 *ds_brightmap;
 extern UINT8 *ds_transmap;
 
-extern UINT8 ds_flatcolor;
-
 struct floatv3_t {
 	float x, y, z;
 };
diff --git a/src/r_plane.cpp b/src/r_plane.cpp
index d2b36bed7..f84448d58 100644
--- a/src/r_plane.cpp
+++ b/src/r_plane.cpp
@@ -13,6 +13,9 @@
 ///        while maintaining a per column clipping list only.
 ///        Moreover, the sky areas have to be determined.
 
+//#include <tracy/tracy/Tracy.hpp>
+
+#include "command.h"
 #include "doomdef.h"
 #include "console.h"
 #include "m_easing.h" // For Easing_InOutSine, used in R_UpdatePlaneRipple
@@ -32,6 +35,8 @@
 #include "z_zone.h"
 #include "p_tick.h"
 
+extern "C" consvar_t cv_debugfinishline;
+
 //
 // opening
 //
@@ -210,21 +215,29 @@ static void R_MapPlane(INT32 y, INT32 x1, INT32 x2)
 		ds_bgofs >>= FRACBITS;
 	}
 
-	pindex = distance >> LIGHTZSHIFT;
-	if (pindex >= MAXLIGHTZ)
-		pindex = MAXLIGHTZ - 1;
-	ds_colormap = planezlight[pindex];
-
-	if (!debugrender_highlight)
+	if (ds_flatlighting)
 	{
-		if (currentplane->extra_colormap)
-			ds_colormap = currentplane->extra_colormap->colormap + (ds_colormap - colormaps);
+		ds_colormap = ds_flatlighting;
+	}
+	else
+	{
+		pindex = distance >> LIGHTZSHIFT;
+		if (pindex >= MAXLIGHTZ)
+			pindex = MAXLIGHTZ - 1;
 
-		ds_fullbright = colormaps;
-		if (encoremap && !currentplane->noencore)
+		ds_colormap = planezlight[pindex];
+
+		if (!debugrender_highlight)
 		{
-			ds_colormap += COLORMAP_REMAPOFFSET;
-			ds_fullbright += COLORMAP_REMAPOFFSET;
+			if (currentplane->extra_colormap)
+				ds_colormap = currentplane->extra_colormap->colormap + (ds_colormap - colormaps);
+
+			ds_fullbright = colormaps;
+			if (encoremap && !currentplane->noencore)
+			{
+				ds_colormap += COLORMAP_REMAPOFFSET;
+				ds_fullbright += COLORMAP_REMAPOFFSET;
+			}
 		}
 	}
 
@@ -359,11 +372,17 @@ static visplane_t *new_visplane(unsigned hash)
 visplane_t *R_FindPlane(fixed_t height, INT32 picnum, INT32 lightlevel,
 	fixed_t xoff, fixed_t yoff, angle_t plangle, extracolormap_t *planecolormap,
 	ffloor_t *pfloor, polyobj_t *polyobj, pslope_t *slope, boolean noencore,
-	boolean ripple, boolean reverseLight, const sector_t *lighting_sector)
+	boolean ripple, boolean reverseLight, const sector_t *lighting_sector,
+	sectordamage_t damage)
 {
 	visplane_t *check;
 	unsigned hash;
 
+	if (!cv_debugfinishline.value)
+	{
+		damage = SD_NONE;
+	}
+
 	if (!slope) // Don't mess with this right now if a slope is involved
 	{
 		if (plangle != 0)
@@ -442,7 +461,8 @@ visplane_t *R_FindPlane(fixed_t height, INT32 picnum, INT32 lightlevel,
 				&& check->plangle == plangle
 				&& check->slope == slope
 				&& check->noencore == noencore
-				&& check->ripple == ripple)
+				&& check->ripple == ripple
+				&& check->damage == damage)
 			{
 				return check;
 			}
@@ -473,6 +493,7 @@ visplane_t *R_FindPlane(fixed_t height, INT32 picnum, INT32 lightlevel,
 	check->slope = slope;
 	check->noencore = noencore;
 	check->ripple = ripple;
+	check->damage = damage;
 
 	memset(check->top, 0xff, sizeof (check->top));
 	memset(check->bottom, 0x00, sizeof (check->bottom));
@@ -551,6 +572,7 @@ visplane_t *R_CheckPlane(visplane_t *pl, INT32 start, INT32 stop)
 		new_pl->slope = pl->slope;
 		new_pl->noencore = pl->noencore;
 		new_pl->ripple = pl->ripple;
+		new_pl->damage = pl->damage;
 		pl = new_pl;
 		pl->minx = start;
 		pl->maxx = stop;
@@ -858,6 +880,7 @@ void R_DrawSinglePlane(visplane_t *pl)
 	debugrender_highlight_t debug = debugrender_highlight_t::SW_HI_PLANES;
 
 	void (*mapfunc)(INT32, INT32, INT32) = R_MapPlane;
+	bool highlight = R_PlaneIsHighlighted(pl);
 
 	if (!(pl->minx <= pl->maxx))
 		return;
@@ -865,7 +888,22 @@ void R_DrawSinglePlane(visplane_t *pl)
 	// sky flat
 	if (pl->picnum == skyflatnum)
 	{
-		R_DrawSkyPlane(pl);
+		if (highlight)
+		{
+			r8_flatcolor = 35; // red
+			dc_lightmap = colormaps;
+
+			for (dc_x = pl->minx; dc_x <= pl->maxx; ++dc_x)
+			{
+				dc_yl = pl->top[dc_x];
+				dc_yh = pl->bottom[dc_x];
+				R_DrawColumn_Flat_8();
+			}
+		}
+		else
+		{
+			R_DrawSkyPlane(pl);
+		}
 		return;
 	}
 
@@ -918,6 +956,7 @@ void R_DrawSinglePlane(visplane_t *pl)
 
 				// Hacked up support for alpha value in software mode Tails 09-24-2002
 				// ...unhacked by toaster 04-01-2021
+				if (!highlight)
 				{
 					INT32 trans = (10*((256+12) - pl->ffloor->alpha))/255;
 					if (trans >= 10)
@@ -1119,11 +1158,20 @@ void R_DrawSinglePlane(visplane_t *pl)
 		planezlight = zlight[light];
 	}
 
+	if (highlight && R_SetSpanFuncFlat(BASEDRAWFUNC))
+	{
+		r8_flatcolor = 35; // red
+		ds_flatlighting = colormaps;
+	}
+	else
+	{
+		R_CheckDebugHighlight(debug);
 
-	R_CheckDebugHighlight(debug);
+		// Use the correct span drawer depending on the powers-of-twoness
+		R_SetSpanFunc(spanfunctype, !ds_powersoftwo, ds_brightmap != NULL);
 
-	// Use the correct span drawer depending on the powers-of-twoness
-	R_SetSpanFunc(spanfunctype, !ds_powersoftwo, ds_brightmap != NULL);
+		ds_flatlighting = NULL;
+	}
 
 	// set the maximum value for unsigned
 	pl->top[pl->maxx+1] = 0xffff;
@@ -1226,3 +1274,8 @@ void R_PlaneBounds(visplane_t *plane)
 	plane->high = hi;
 	plane->low = low;
 }
+
+boolean R_PlaneIsHighlighted(const visplane_t *pl)
+{
+	return pl->damage == SD_DEATHPIT || pl->damage == SD_INSTAKILL;
+}
diff --git a/src/r_plane.h b/src/r_plane.h
index 2a77dcfea..2d2f5b04e 100644
--- a/src/r_plane.h
+++ b/src/r_plane.h
@@ -20,6 +20,7 @@ extern "C" {
 
 #include "screen.h" // needs MAXVIDWIDTH/MAXVIDHEIGHT
 #include "r_data.h"
+#include "r_defs.h"
 #include "r_textures.h"
 #include "p_polyobj.h"
 
@@ -60,6 +61,7 @@ struct visplane_t
 
 	boolean noencore;
 	boolean ripple;
+	sectordamage_t damage;
 };
 
 extern visplane_t *visplanes[MAXVISPLANES];
@@ -88,7 +90,7 @@ void R_ClearFFloorClips (void);
 void R_DrawPlanes(void);
 visplane_t *R_FindPlane(fixed_t height, INT32 picnum, INT32 lightlevel, fixed_t xoff, fixed_t yoff, angle_t plangle,
 	extracolormap_t *planecolormap, ffloor_t *ffloor, polyobj_t *polyobj, pslope_t *slope, boolean noencore,
-	boolean ripple, boolean reverseLight, const sector_t *lighting_sector);
+	boolean ripple, boolean reverseLight, const sector_t *lighting_sector, sectordamage_t damage);
 visplane_t *R_CheckPlane(visplane_t *pl, INT32 start, INT32 stop);
 void R_ExpandPlane(visplane_t *pl, INT32 start, INT32 stop);
 void R_PlaneBounds(visplane_t *plane);
@@ -108,6 +110,8 @@ void R_CalculateSlopeVectors(void);
 // Sets the slope vector pointers for the current tilted span.
 void R_SetTiltedSpan(INT32 span);
 
+boolean R_PlaneIsHighlighted(const visplane_t *pl);
+
 struct visffloor_t
 {
 	visplane_t *plane;
diff --git a/src/r_portal.c b/src/r_portal.c
index d40bd39d1..0a4a645e1 100644
--- a/src/r_portal.c
+++ b/src/r_portal.c
@@ -301,7 +301,7 @@ void Portal_AddSkyboxPortals (void)
 	{
 		for (pl = visplanes[i]; pl; pl = pl->next)
 		{
-			if (pl->picnum == skyflatnum)
+			if (pl->picnum == skyflatnum && !pl->damage)
 			{
 				Portal_AddSkybox(pl);
 
diff --git a/src/r_segs.cpp b/src/r_segs.cpp
index 89b215808..27c25ce7d 100644
--- a/src/r_segs.cpp
+++ b/src/r_segs.cpp
@@ -11,6 +11,9 @@
 /// \file  r_segs.c
 /// \brief All the clipping: columns, horizontal spans, sky columns
 
+//#include <tracy/tracy/Tracy.hpp>
+
+#include "command.h"
 #include "doomdef.h"
 #include "r_local.h"
 #include "r_sky.h"
@@ -29,6 +32,8 @@
 #include "r_draw.h"
 #include "k_terrain.h"
 
+extern "C" consvar_t cv_debugfinishline;
+
 #define HEIGHTBITS              12
 #define HEIGHTUNIT              (1<<HEIGHTBITS)
 
@@ -2248,7 +2253,9 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			|| frontsector->extra_colormap != backsector->extra_colormap
 			|| (frontsector->ffloors != backsector->ffloors && !Tag_Compare(&frontsector->tags, &backsector->tags))
 			// Portals block traversal behind them
-			|| g_portal)
+			|| g_portal
+			// Highlighting death pits
+			|| (cv_debugfinishline.value && frontsector->damagetype != backsector->damagetype))
 		{
 			markfloor = true;
 		}
@@ -2283,7 +2290,9 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			|| frontsector->extra_colormap != backsector->extra_colormap
 			|| (frontsector->ffloors != backsector->ffloors && !Tag_Compare(&frontsector->tags, &backsector->tags))
 			// Portals block traversal behind them
-			|| g_portal)
+			|| g_portal
+			// Highlighting death pits
+			|| (cv_debugfinishline.value && frontsector->damagetype != backsector->damagetype))
 		{
 				markceiling = true;
 		}
@@ -2860,7 +2869,7 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			{
 				for (rover = backsector->ffloors; rover && i < MAXFFLOORS; rover = rover->next)
 				{
-					if (!(rover->fofflags & FOF_EXISTS) || !(rover->fofflags & FOF_RENDERPLANES))
+					if (!(rover->fofflags & FOF_EXISTS) || (!cv_debugfinishline.value && !(rover->fofflags & FOF_RENDERPLANES)))
 						continue;
 					if (rover->norender == leveltime)
 						continue;
@@ -2917,7 +2926,7 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 			{
 				for (rover = frontsector->ffloors; rover && i < MAXFFLOORS; rover = rover->next)
 				{
-					if (!(rover->fofflags & FOF_EXISTS) || !(rover->fofflags & FOF_RENDERPLANES))
+					if (!(rover->fofflags & FOF_EXISTS) || (!cv_debugfinishline.value && !(rover->fofflags & FOF_RENDERPLANES)))
 						continue;
 					if (rover->norender == leveltime)
 						continue;
diff --git a/src/screen.c b/src/screen.c
index 21a6ad00e..1fcbc6d36 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -258,11 +258,12 @@ void R_SetSpanFunc(size_t id, boolean npo2, boolean brightmapped)
 {
 	I_Assert(id < COLDRAWFUNC_MAX);
 
-	if (spanfuncs_flat[id] != NULL && debugrender_highlight != 0)
+	if (debugrender_highlight != 0 && R_SetSpanFuncFlat(id))
 	{
-		spanfunc = spanfuncs_flat[id];
+		return;
 	}
-	else if (spanfuncs_npo2[id] != NULL && npo2 == true)
+
+	if (spanfuncs_npo2[id] != NULL && npo2 == true)
 	{
 		spanfunc = spanfuncs_npo2[id];
 	}
@@ -278,6 +279,20 @@ void R_SetSpanFunc(size_t id, boolean npo2, boolean brightmapped)
 	}
 }
 
+boolean R_SetSpanFuncFlat(size_t id)
+{
+	I_Assert(id < SPANDRAWFUNC_MAX);
+
+	if (spanfuncs_flat[id] == NULL)
+	{
+		return false;
+	}
+
+	spanfunc = spanfuncs_flat[id];
+
+	return true;
+}
+
 boolean R_CheckColumnFunc(size_t id)
 {
 	size_t i;
diff --git a/src/screen.h b/src/screen.h
index 70455885f..f8ab2dc1b 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -225,6 +225,7 @@ void SCR_SetDrawFuncs(void);
 // Set current column / span drawers
 void R_SetColumnFunc(size_t id, boolean brightmapped);
 void R_SetSpanFunc(size_t id, boolean npo2, boolean brightmapped);
+boolean R_SetSpanFuncFlat(size_t id); // flat color
 
 // Compare current column drawer
 boolean R_CheckColumnFunc(size_t id);