Fixes ayylmaos being ayytaurs, skeletons being skeletaurs and basically every other humanoid mob from having weird taur/tail features.

code/datums/bodypart_overlays/mutant_bodypart_overlay.dm

@@ -33,9 +33,12 @@
 		stack_trace("adding a [parent.type] to a [receiver.type] when it shouldn't be!")
 
 	if(imprint_on_next_insertion) //We only want this set *once*
-		var/feature_name = receiver.dna.features[feature_key] || receiver.dna.species.mutant_organs[parent.type]
+		/* DOPPLER EDIT START -  Uses special_feature_key from modular instead of normal feature_keys */
+		var/dna_feature_key = special_feature_key || feature_key
+		var/feature_name = receiver.dna.features[dna_feature_key] || receiver.dna.species.mutant_organs[parent.type] // originally: var/feature_name = receiver.dna.features[feature_key] || receiver.dna.species.mutant_organs[parent.type]
+		/* DOPPLER EDIT END */
 		if (isnull(feature_name))
-			stack_trace("[type] has no default feature name for organ [parent.type]!")
+			// DOPPLER REMOVAL (stack_trace works off of mutant part assumptions that aren't compatible with our own mutant part system) - stack_trace("[type] has no default feature name for organ [parent.type]!")
 			feature_name = get_consistent_feature_entry(get_global_feature_list()) //fallback to something
 		set_appearance_from_name(feature_name)
 		imprint_on_next_insertion = FALSE

code/modules/mob/living/carbon/human/dummy.dm

@@ -113,8 +113,10 @@ INITIALIZE_IMMEDIATE(/mob/living/carbon/human/dummy)
 /proc/create_consistent_human_dna(mob/living/carbon/human/target)
 	target.dna.features[FEATURE_MUTANT_COLOR] = COLOR_VIBRANT_LIME
 	target.dna.features[FEATURE_ETHEREAL_COLOR] = COLOR_WHITE
+	/* DOPPLER REMOVAL START - Removes applying ALL consistent features just because they exist
 	for(var/feature_key in SSaccessories.feature_list)
 		target.dna.features[feature_key] = get_consistent_feature_entry(SSaccessories.feature_list[feature_key])
+	DOPPLER REMOVAL END */
 	// DOPPLER ADDITION START - Fix tri color features in dummies
 	target.dna.features[FEATURE_EARS_COLORS] = DEFAULT_MATRIXED_FEATURE_COLORS
 	target.dna.features[FEATURE_MARKINGS_COLORS] = DEFAULT_MATRIXED_FEATURE_COLORS

code/modules/surgery/organs/external/tails.dm

@@ -71,9 +71,17 @@
 	if(!tail_spine_key)
 		return
 
+	/* DOPPLER ADDITION START - Fixes tail spines throwing runtimes when spawning humanoid mobs/corpses with tails
+	 * The tail spines overlay is dependent on the owner's DNA, which may not be set yet.
+	 * If the owner doesn't have a valid DNA, don't insert the tail spines overlay.*/
+	var/obj/item/organ/spines/owner_spines = bodypart.owner.get_organ_slot(ORGAN_SLOT_EXTERNAL_SPINES)
+	var/feature_name = bodypart.owner.dna.features[FEATURE_SPINES] || bodypart.owner.dna.species.mutant_organs[owner_spines?.type]
+	if(!feature_name || feature_name == SPRITE_ACCESSORY_NONE)
+		return
+	/* DOPPLER ADDITION END */
 	tail_spines_overlay = new
 	tail_spines_overlay.tail_spine_key = tail_spine_key
-	var/feature_name = bodypart.owner.dna.features[FEATURE_SPINES] //tail spines don't live in DNA, but share feature names with regular spines
+	//DOPPLER REMOVAL: var/feature_name = bodypart.owner.dna.features[FEATURE_SPINES] //tail spines don't live in DNA, but share feature names with regular spines
 	tail_spines_overlay.set_appearance_from_name(feature_name)
 	bodypart.add_bodypart_overlay(tail_spines_overlay)
 

modular_doppler/modular_customization/organs/mutant_bodypart_overlay.dm

@@ -132,5 +132,14 @@
 /datum/bodypart_overlay/mutant/proc/get_feature_key_for_overlay()
 	return sprite_datum?.key || feature_key
 
+/// Returns the DNA feature which controls whether an organ type's overlay is present.
+/proc/get_bodypart_overlay_dna_feature_key_from_type(obj/item/organ/organ_type)
+	if(isnull(organ_type))
+		return null
+	var/datum/bodypart_overlay/mutant/overlay_type = initial(organ_type.bodypart_overlay)
+	if(isnull(overlay_type))
+		return null
+	return initial(overlay_type.special_feature_key) || initial(overlay_type.feature_key)
+
 #undef MAX_MATRIXED_COLORS
 #undef ALPHA_OPAQUE

modular_doppler/modular_customization/preferences/tail.dm

@@ -1,31 +1,52 @@
 /datum/dna
 	///	This variable is read by the regenerate_organs() proc to know what organ subtype to give
-	var/tail_type = NO_VARIATION
+	/// Null until a tail choice is applied, NO_VARIATION for an explicit opt-out, or a tail category to generate.
+	var/tail_type
 
 /datum/species/regenerate_organs(mob/living/carbon/target, datum/species/old_species, replace_current = TRUE, list/excluded_zones, visual_only = FALSE, replace_missing = TRUE)
-	. = ..()
 	if(target == null)
-		return
+		return ..()
+
+	// The normal organ code will not add a tail while its DNA feature is set to "None".
+	// Read which feature the species' tail overlay uses directly from its type, then set that feature to the species default before calling the normal organ code below.
+	// Without this, generic mobs without player preferences will not get a tail when their species should.
+	var/use_species_default_tail = FALSE
+	if(isnull(target.dna.tail_type)) // always false when the target has prefs
+		var/obj/item/organ/species_tail_type = get_mutant_organ_type_for_slot(ORGAN_SLOT_EXTERNAL_TAIL)
+		if(species_tail_type) // always false when a species doesn't normally have a tail
+			var/default_tail_appearance = mutant_organs[species_tail_type]
+			var/tail_feature_key = get_bodypart_overlay_dna_feature_key_from_type(species_tail_type)
+			if(tail_feature_key && default_tail_appearance)
+				target.dna.features[tail_feature_key] = default_tail_appearance
+				use_species_default_tail = TRUE
+
+	. = ..()
+	// The parent has now handled the species' usual tail. The customization branches below are only for player-prefs tail choices, including an explicit preference to have no tail.
+	if(use_species_default_tail)
+		return .
+
 	if(!ishuman(target))
 		return
 
-	if(can_regenerate_mutant_feature(FEATURE_TAIL_LIZARD) && target.dna.features[FEATURE_TAIL_LIZARD] != /datum/sprite_accessory/blank::name)
+	// Because we both have None & Null as possible values we check target.dna.features twice. First for null, then afterwards for "None"
+	// can_regenerate_mutant_feature() is used to prevent giving mutant parts to species on GLOB.species_blacklist_no_mutant
+	if(target.dna.features[FEATURE_TAIL_LIZARD] && can_regenerate_mutant_feature(FEATURE_TAIL_LIZARD) && target.dna.features[FEATURE_TAIL_LIZARD] != /datum/sprite_accessory/blank::name)
 		var/obj/item/organ/replacement = SSwardrobe.provide_type(/obj/item/organ/tail/lizard)
 		replacement.Insert(target, special = TRUE, movement_flags = DELETE_IF_REPLACED)
 		return .
-	else if(can_regenerate_mutant_feature(FEATURE_TAIL_CAT) && target.dna.features[FEATURE_TAIL_CAT] != /datum/sprite_accessory/blank::name)
+	else if(target.dna.features[FEATURE_TAIL_CAT] && can_regenerate_mutant_feature(FEATURE_TAIL_CAT) && target.dna.features[FEATURE_TAIL_CAT] != /datum/sprite_accessory/blank::name)
 		var/obj/item/organ/replacement = SSwardrobe.provide_type(/obj/item/organ/tail/cat)
 		replacement.Insert(target, special = TRUE, movement_flags = DELETE_IF_REPLACED)
 		return .
-	else if(can_regenerate_mutant_feature(FEATURE_TAIL_MONKEY) && target.dna.features[FEATURE_TAIL_MONKEY] != /datum/sprite_accessory/blank::name)
+	else if(target.dna.features[FEATURE_TAIL_MONKEY] && can_regenerate_mutant_feature(FEATURE_TAIL_MONKEY) && target.dna.features[FEATURE_TAIL_MONKEY] != /datum/sprite_accessory/blank::name)
 		var/obj/item/organ/replacement = SSwardrobe.provide_type(/obj/item/organ/tail/monkey)
 		replacement.Insert(target, special = TRUE, movement_flags = DELETE_IF_REPLACED)
 		return .
-	else if(can_regenerate_mutant_feature(FEATURE_TAIL_FISH) && target.dna.features[FEATURE_TAIL_FISH] != /datum/sprite_accessory/blank::name)
+	else if(target.dna.features[FEATURE_TAIL_FISH] && can_regenerate_mutant_feature(FEATURE_TAIL_FISH) && target.dna.features[FEATURE_TAIL_FISH] != /datum/sprite_accessory/blank::name)
 		var/obj/item/organ/replacement = SSwardrobe.provide_type(/obj/item/organ/tail/fish)
 		replacement.Insert(target, special = TRUE, movement_flags = DELETE_IF_REPLACED)
 		return .
-	else if((can_regenerate_mutant_feature(FEATURE_TAIL_OTHER) && target.dna.features[FEATURE_TAIL_OTHER] != /datum/sprite_accessory/blank::name) && (target.dna.tail_type != NO_VARIATION))
+	else if((target.dna.features[FEATURE_TAIL_OTHER] && can_regenerate_mutant_feature(FEATURE_TAIL_OTHER) && target.dna.features[FEATURE_TAIL_OTHER] != /datum/sprite_accessory/blank::name) && (target.dna.tail_type && target.dna.tail_type != NO_VARIATION))
 		var/obj/item/organ/organ_path = text2path("/obj/item/organ/tail/[target.dna.tail_type]")
 		var/obj/item/organ/replacement = SSwardrobe.provide_type(organ_path)
 		replacement.Insert(target, special = TRUE, movement_flags = DELETE_IF_REPLACED)
@@ -715,8 +736,9 @@
 	feature_key_sprite = "tail"
 
 /datum/bodypart_overlay/mutant/tail/color_images(list/image/overlays, layer, obj/item/bodypart/limb)
-	if((sprite_datum.color_src == USE_ONE_COLOR) && length(limb.owner?.dna.features[FEATURE_TAIL_COLORS]))
-		draw_color = limb.owner?.dna.features[FEATURE_TAIL_COLORS][1]
-	else
-		draw_color = limb.owner?.dna.features[FEATURE_TAIL_COLORS]
+	var/list/tail_colors = limb.owner?.dna.features[FEATURE_TAIL_COLORS]
+	// Preference colors override the tail's inherited limb color. Generic mobs do not have this
+	// preference data, so retaining draw_color makes their native tail match their mutant color.
+	if(length(tail_colors))
+		draw_color = sprite_datum.color_src == USE_ONE_COLOR ? tail_colors[1] : tail_colors
 	return ..()