Baruka's Dagger
Weapon (Dagger), Rare (Requires Attunement)
You gain a +1 bonus to attack and damage rolls made with this magic weapon.
Improved Agility. You gain advantage to acrobatics checks and dexterity saving throws while you are holding the dagger.
Swift Steps. Increase walking speed by 10 ft while holding the dagger.
Warden's Necklace
Wonderous Item, Very Rare (Requires Attunement)
You gain a +2 to spell attack rolls and your passive perception increases by +2.
K9 Senses. Your senses have become sharper, you now have advantage on wisdom (Perception) checks that involve smell and hearing.
Red Knight helmet
Armor, Rare (Requires attunement)
This item raises both your strength and constitution scores by +2. Your AC also increases by +2 while wearing the helmet.
Damage debuff. You become resistant to non-magical piercing, slashing, and bludgeoning. You also become resistant to magical piercing.
Demon Monarch's earring
Wonderous item, Very Rare (Requires Attunement)
This item raises both your strength and constitution scores by +2. You gain the ability to see normally in darkness, both magical and nonmagical, to a distance of 120 feet. Your sight also pierces even the toughest of veils, you gain a range of True Sight up to 30 feet.
Demon Monarch's necklace
*Wonderous Item, Rare (Requires Attunement)
While attuned to Demon Monarch's Necklace, you become resistant to fire. While the necklace is worn, you gain the ability to speak any language.
Demon Monarch's ring
Wonderous Item, Legendary (Requires Attunement)
This item raises both your wisdom and intelligence scores by +2.
The ring has 8 charges. It regains 1d4 + 2 expended charges daily at dawn.
You can expend 3 charges to cast Summon Lesser Demons or 4 charges to cast Summon Greater Demon. For each extra charge used above the original cost allows you to cast either spell at a higher level up to a maximum of 9th level.
While attuned to the Demon Monarch's ring you gain the spells Summon Lesser Demons and Summon Greater Demon if you do not already have them, the demons that are summon cannot lose loyalty to you who are attuned to the ring.
Set Bonus 1 When 2 of the Demon Monarch items are attuned, increases the stats by 4. You can go beyond 20 but not 30.
Set Bonus 2 When 3 of the Demon Monarch items are attuned, increase the stats by 6. you can go beyond 20 but not 30.
Solitary Item. When you gain the third of the Demon Monarch items in no particular order, they combine to take up only a single attunement slot.
Magic of the Demon Monarch. When you complete the first Set Bonus when attuning 2 items together you gain the ability to cast Lightning Arrow (5th level). When you cast Lightning Arrow you do not need a bow and arrow, but instead like Zeus would with his lighning bolts. Once you use this spell, you cannot cast it again until you finish a long rest. When you complete the second Set Bonus when attuning all 3 items together you gain the ability to cast Chain Lightning and Prismatic Spray (Yellow), once you cast either spell you cannot do so until you finish a long rest.
Demon King's daggers:
Weapon dagger, Legendary (Requires Attunement)
You gain a +3 to attack and damage rolls made with per magic weapon.
Set Bonus. Two as One When you have both daggers equipped, your dexterity (or strength) score increases to a maximum of 24. The damage dice dealt with these daggers both attuned increases to 3d8 piercing + 3d6 lightning damage per dagger. These daggers also take up a single attunement slot when both are attuned.
Twin Dagger 1. This dagger harnesses negative emotions to strike opponents down in the blink of an eye. The critical hit range of the twin dagger is increased to 19-20.
Twin Dagger 2. This dagger thrives through the very chaotic nature of the demon it was created from. You have advantage against any spell, magical effect or natural trait that both devils and demons try to cast at you while twin dagger 2 is attuned. This twin dagger's damage is increased to 3d4.
Demon king's longsword
Weapon longsword, Very Rare (Requires Attunement)
You gain a +2 to attack and damage rolls made with this magic weapon and a hit deals an additional 4d6 lightning damage.
Shocking Display. Whenever an attack is made with this weapon, everyone in a 10 ft radius around the attacked target must make a Dexterity Saving Throw DC 17. On a failed save the target takes 2d6 additional lightning damage and is paralyzed. Any creature who successfully saves takes half as much and is not paralyzed.
Edit Notes:
Removed dexterity increase to Baruka's dagger. Removed dexterity and intelligence increase to Demon Monarch item. Changed Warden's Necklace rarity and attunement requirement.
Art Credit
Baruka's Dagger: Art by Kevinmakescoolthings on Thingiverse
Warden's Necklace:
Red Knight Helmet/Blood-Red Commander Igris: Art by vertei on redbubble
Demon Monarch's earring: Chugong Solo Leveling Author
Demon Monarch's necklace:
Demon Monarch's ring:
Demon King's Daggers: Art by hudi_baba from reddit
Demon King's Longsword: Art by ragingdonut_ from reddit