Sablevein, the Rust Wyrm

Traits

• Legendary Resistance (3/Day). If Sablevein fails a saving throw, it can choose to succeed instead. Each time it does, a fist-sized scale falls from its flank and crumbles to red powder.
• Ironsense. Sablevein knows the location and approximate mass of every piece of unworked metal within 1 mile of it, and it can tell worked steel from ore by smell alone.
• Corroding Presence. Any nonmagical metal object that begins its turn within 10 feet of Sablevein and is not being worn or carried is reduced to rust. A creature wearing metal armour that ends its turn within 10 feet of the wyrm must succeed on a DC 20 Constitution saving throw or take 10 (3d6) acid damage as its armour heats and flakes.
• Hoard of Ruin. While in its lair, Sablevein regains 20 hit points at the start of each of its turns as long as unclaimed metal remains in the hoard. A hoard stripped of metal ends this trait until the wyrm replenishes it.

Spellcasting

Sablevein, the Rust Wyrm is an 18th-level spellcaster. Their spellcasting ability is Charisma (spell save DC 19, +11 to hit with spell attacks).

• Cantrips (at will). Mending
• 1st level (4 slots). Shield
• 2nd level (3 slots). Heat Metal
• 3rd level (3 slots). Counterspell
• 4th level (3 slots). Fabricate
• 5th level (2 slots). Wall of Stone

Actions

• Multiattack. Sablevein makes three attacks: one Bite attack and two Claw attacks. It can replace one Claw attack with a Tail attack.
• Bite. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 9 (2d8) acid damage. Sablevein’s teeth are not enamel but layered iron, and they shed flakes of rust into every wound they open.
• Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 15 (2d6 + 8) slashing damage. If the target is wearing metal armour or carrying a metal shield, that item takes a permanent and cumulative -1 penalty to the AC it offers. Armour reduced to a 0 bonus, or a shield to -2, is destroyed.
• Tail. Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage. The wyrm’s tail drags a wake of iron filings behind it.
• Rust Breath (Recharge 5-6). Sablevein exhales a 60-foot cone of red, gritty vapour. Every nonmagical metal object in the area that is not being worn or carried is destroyed outright. Each creature in the area must make a DC 20 Dexterity saving throw, taking 56 (16d6) acid damage on a failed save, or half as much damage on a successful one.

Bonus Actions

• Shed Scale. Sablevein sloughs a plate of rusted scale into a space within 10 feet of it. The space becomes difficult terrain, and a creature that enters it for the first time on a turn takes 7 (2d6) piercing damage from the shards. The scale crumbles at the start of the wyrm’s next turn.

Reactions

• Oxidize. Trigger: A creature within 20 feet of Sablevein hits it with a metal weapon. The weapon rusts in the attacker’s hands. It takes a permanent -1 penalty to damage rolls, and a weapon reduced to -3 is destroyed. Magic weapons are unaffected but are slick with rust until cleaned.
• Wing Buffet. Trigger: A creature Sablevein can see moves into a space within 15 feet of it. Sablevein beats one wing. The triggering creature must succeed on a DC 22 Strength saving throw or be pushed 15 feet away and knocked prone.

Legendary Actions

Sablevein, the Rust Wyrm can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time, and only at the end of another creature's turn. Sablevein regains spent legendary actions at the start of their turn.

• Ironsense. Sablevein makes a Wisdom (Perception) check, and until the end of its next turn it knows the location of every creature carrying metal within 120 feet, even behind total cover.
• Tail Attack. Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage. The wyrm’s tail drags a wake of iron filings behind it.
• Corroding Wings (Costs 2 Actions). Sablevein beats its wings and flies up to half its speed. Each creature within 15 feet of the space it left must succeed on a DC 22 Dexterity saving throw or take 14 (4d6) acid damage from the storm of rust.

Lair Actions

• The Vein Opens. A seam of raw ore splits the floor. Each creature on the ground within 30 feet of the seam must succeed on a DC 20 Dexterity saving throw or fall prone as the stone shifts, and any metal weapon dropped in the area is drawn into the seam and lost.
• Red Air. Rust-laden dust fills a 20-foot-radius sphere centred on a point Sablevein can see within 120 feet. The area is lightly obscured, and a creature that starts its turn there must succeed on a DC 20 Constitution saving throw or be unable to speak above a whisper until the end of its next turn.

Regional Effects

• Nothing Iron Keeps an Edge. Nonmagical metal left unattended overnight within the region is found pitted and orange by morning. Blacksmiths in the region work only in bronze, bone and stone, and say so as though it were always the fashion. The effect extends 6 miles from the lair.
• The Ground Answers. Compasses spin, lodestones lose their pull, and miners within the region report hearing a slow scraping beneath them at the same hour each night. The effect extends 6 miles from the lair.