The Cat God

Weapons from The Cat God (Nightmare) seasonal dungeon, available to players only during Halloween, use the same skins as Quality 0 White weapons. Outfit shown is the Baron / Baroness Samedi set rewarded by completing The Cat God mission, plus top hat.

Ancient Mayan Weapon

Source: (2013) The Road to Xibalba dungeon (Normal & Nightmare mode) during the Ever-Ending Days event.
Source: (2012) World drop from Mayan mobs during the End of Days event.
Skins: The Ancient Mayan Sword skin is also available as a Q6 Blue from crafting, the Council of Venice Envoy in the Blue Mountains, and the Weapons Quartermaster in Faction HQs.

Slaughterhouse

Slaughterhouse Soviet tech skins are available on Elite or Nightmare mode, depending on the weapon. They can also be purchased as a Weapon Mould in the item store. Outfit worn is the Red Hand Winter Uniform from the Master Planner achievement.

The rare skins available only on Nightmare mode are: Re-Purposed Scythe blade, Mara’s Book of Names blood focus and Tsar Gun shotgun.

Nightmare mode Slaughterhouse also drops Kyshtym Revolver which shares a skin with the Walther PPKs from The Facility Elite, and the Fangs fist weapon which have the same skin as Meteor Shard from The Facility Elite.

Thank you Shaun2406 for the screenshots.

Hell Eternal

Weapon skins from Hell Eternal are available on Elite or Nightmare mode, depending on the weapon. They can also be purchased as a Weapon Mould in the item store. Outfit worn is the Infernal Finery from the Master Planner achievement.

On Nightmare mode, there are four unique skins; the Creepy Doll Elementalism focus, Bone-Saw blade, Misery pistols and Grimoire of Foul Gods blood magic focus.

Thank you Shaun2406 for the screenshots.

The Facility

Soviet tech weapon skins from The Facility are available on Elite or Nightmare mode, depending on the weapon. They can also be purchased as a Weapon Mould in the item store. Outfit worn is the Red Hand Uniform from the Master Planner achievement.

On Nightmare mode, Halina Ilyushin can drop three rare skins: Basov’s Backup pistols, Jacob’s Prongs fist and the Shield of Barbarossa chaos focus.

Nightmare mode Facility also drops the blood focus Lilith’s Lab Notes which shares a skin with Baba Yaga’s Broken Tooth from SH Elite, and Prokhorov’s New Toy which shares a skin with the Thumper shotgun from SH Elite.

Thank you Shaun2406 for the screenshots.

Hell Fallen

All Hell Fallen weapon skins can be acquired on Normal dungeon mode; they are also available as a Weapon Mould in the item store. Outfit worn is Hellpunk Casual from the Master Planner achievement.

Thank you Shaun2406 for the screenshots.

The Ankh

All Ankh weapon skins can be acquired on Normal dungeon mode; they are also available as a Weapon Mould in the item store. Outfits worn are Spelunking Gear and the Sycoil Jumpsuit from the Master Planner achievements.

Thank you Shaun2406 for the screenshots.

The Darkness War

All Darkness War weapon skins can be acquired on Normal dungeon mode; they are also available as a Weapon Mould in the item store. Outfit worn is the Dawnbringer Garb from the Master Planner achievement.

Thank you Shaun2406 for the screenshots.

Hell Raised

All Hell Raised weapon skins can be acquired on Normal dungeon mode; they are also available as a Weapon Mould in the item store. Outfit worn is the Demonskin Coat from the Master Planner achievement.

Thank you Shaun2406 for the screenshots.

The Polaris

All Polaris weapon skins can be acquired on Normal dungeon mode; they are also available as a Weapon Mould in the item store. Outfit worn is the Sycoil Jumpsuit from the Master Planner achievement.

Thank you Shaun2406 for the screenshots.