Scale Mail

The Scale Mail also known as the Armor of the Dragon Emperor is the Overdrive armor of Arthur's Boosted Pump and Vali's Divine Dividing.

Summary
Arthur first activated his partially-imperfect version of Scale Mail in Volume 2 by making a pact with Ddraig by giving his left hand to the Dragon.

When Vali appeared in Volume 3, he was already in his Overdrive form, a perfect version of the Scale Mail.

In Volume 4, when Arthur fought against Vali, Arthur used a bracelet given to him by Azazel which allowed him to use the partially-imperfect version of Scale Mail for less than 15 minutes.

Arthur achieved his perfected version of the Scale Mail in Volume 5 after a subjection lesson with Mina. After gaining the Scale Mail, it soon became the primary battle form for both Arthur and Vali.

Abilities
The Scale Mail generates a Dragon Armor while drastically increasing the user's power, abilities, speed, and defense. It also temporarily allows the user to use the power of the Boosted Pump and Divine Dividing without the 10-second interval. The armor is also capable of repairing itself from almost any damage it takes.

In Volume 15, it is suggested that the Scale Mail can (at least temporarily) protect the wearer, and allow them to survive within the Dimensional Gap.

Weaknesses
Wearing the armor and the duration it stays activated depends on the users physical and mental condition, otherwise it can be severely lethal to them, so the Sacred Gear forcefully removes the armor when the wearer reaches their limit as a fail-safe.

How much the armor repairs itself depends on the wearer's stamina.

Even with the protection of the Scale Mail, the wielders are still susceptible to Dragon-slaying attacks such as dragon-slayer magic and weapons infused with said magic.

When Arthur first attained his Overdrive, it had the following weaknesses: As of Volume 16, Arthur has already overcome these weaknesses.
 * 1) Activating Scale Mail takes approximately two minutes, during which a countdown begins on the gauntlet gem. During this period, he cannot cancel the process, or use other abilities such as "Boost" or "Transfer".
 * 2) Initially, it could only be used for half an hour once a day, and his Ancient Gear becomes powerless for the rest of the day. Also, in Scale Mail mode, each use of the "Boost" and "Gift" ability reduces the remaining amount of time of his Overdrive.

Red Scale Mail
The Scale Mail of Boosted Pump used by Arthur creates a Red Dragon Armor with green jewels that covers the body of the user. This armor has a pair of rocket thrusters at the back that gives a temporary boost of speed and flight, assisted by the retractable Dragon wings that comes out of it. In this form, Arthur can double his power any time he wishes, but at the cost of a large amount of stamina and magical power.

Incursio Move Andernach
In Volume 6, Myrddin Beelzebub, one of the Seven Great Satans and creator of the Evil Pieces system, remodels Arthur's King/Master Piece, as well as gifts him with three transfer pieces, so that he can use the Pawn's promotion to change to a bishop, rook or knight. During Promotion, Arthur can now use Incursio Move Andernach to change his Scale Mail armor into other forms.

Cardinal Crimson Incursio
Cardinal Crimson Incursio, also known as the True Crimson Invasion Dragon Emperor, is Scale Mail's Queen form that debuted in Volume 10 during Arthur's Rating Game battle against Sairaorg Behemoth and Leohart. It changes the color of Arthur's armor to crimson. Cardinal Crimson Incursio incorporates all three Evil Pieces traits, making it the most balanced and most powerful form of Arthur's Scale Mail. However, for full use, it requires all Incursio Move Andernach forms to be fully developed and mastered before it can be completely stabilized, and its full power brought out.

It is stated to be Arthur's answer to an alternative for the Juggernaut Drive.

To enter into Cardinal Crimson Incursio, Arthur recites the incantation, after which the Boosted Gear announces "Cardinal Invasion Drive!"

Diabolus Dragon Beast
 is a form that is exclusive to Arthur. This is due to the fact that his body is made from Scarlet Grand's flesh, which enables Arthur to temporarily borrow his mother's and Wagyl's powers. In this form, the armor becomes "organic" and changes shape and color from pure crimson to a mix of crimson, white and black. Additionally, this form gains a total of six wings, each one containing a cannon. Diabolus Dragon Beast grants Arthur Ophis's power of infinity and Wagyl's power of dreams, enhancing him to the point that he was easily able to overwhelm Rizevim Livan Lucifer, even with his Sacred Gear Canceller Advanced. Arthur can use a finishing move called the Longineus Infinity Blaster, a move using all the cannons hidden in its wings. The Longineus Blaster is so powerful that the blast left Rizevim injured to a extent that his body was almost fatally damaged. According Rizevim, Diabolus Dragon Beast has similar features to the Juggernaut Drive without the ominous aura and after his defeat he speculated that Arthur is on a level of a Super Devil, with both him and later Azazel dubbing it as a Transcendental Overdrive. However, the time Arthur can spend in DxDxB mode is very limited, and after the armor is released, Arthur experiences immense pain throughout his entire body.

Super Gigantic Overdrive
Super Gigantic Overdrive ( 超巨大禁手 ) is a form Arthur attained in Volume 15 by receiving Scarlet Grand's help, in which Arthur reproduces the size of Scarlet Grand which he uses to destroy Jabberwocky, a monstrous beast created by Annihilation Maker. In this form, he gains highly destructive powers such as the forbidden and sealed power of the Longinus Smasher, an attack that can cause an area in Hell to disappear without a trace.

Crimson Vampiria Dragonar : An alternate form of the Boosted Pump Scale Mail armor created by Mina and Arthur. Arthur uses his Red Wyverns and sync his aura with Mina's and the Wyverns that attaches onto herself to create her own version of the Scale Mail armor that fits her perfectly. The armor acts just like the original, enhancing Mina's abilities and giving her the ability to utilize Boost, Transfer, and Penetrate until she reaches her limit.

Crimson Clear Dragonar (クリムゾン・クリア・ドラグナー, Kurimuzon Kuria Doragunā): Tomoe's own variation of the Scale Mail armor, which she gained by syncing her aura with Arthur's that uses his Red Wyverns to attach themselves onto her body which shifts into the form of armor. Like the original, it has all of the same functions of Boost, Transfer and Penetrate. This is noted to be similar to Mina's own Crimson Vampiria Dragonar, yet different from it.

Crimson Succubus Dragonar (クリムゾン・サキュバス・ドラグナー, Kurimuzon Sakyubasu Doragunā):

White Scale Mail
The Scale Mail of Divine Dividing used by Vali creates a White Dragon Armor with blue jewels that covers the body of the user. In this form, Vali can halve the power of his opponents any time he wishes after he touches them until reaching his limits, but at the cost of a large amount of stamina and magical power.

Caesar Juggernaut Overdrive
Caesar Juggernaut Overdrive is a new form attained by Vali in Volume 12. It changes the color of his armor to silver. It was first used against Plouton. This form does not consume his lifespan, but consumes stamina and magical power at a very fast rate, to the extent where just using it in a short fight against Plouton caused Vali to breathe heavily from exhaustion. According to Vali, his Caesar Juggernaut Overdrive can even reach Gods in terms of power output but he can't maintain this form for a long time due to the form's massive stamina consumption rate. Upon seeing this form in combat, Cao Cao speculated that Vali may have reached the Super Devil level.

To enter into Caesar Juggernaut Overdrive, Vali recites the incantation, after which the Divine Dividing announces "Juggernaut Over Drive!"

Diabolus Dragon Beast
  is a form that is granted to Vali by Ophis in Volume 21. Just like Arthur's Diabolus Dragon Beast, this armor is organic and is a mixture of silver, orange, white and black. The power granted is immense, enough to allow Vali to defeat a Heavenly Dragon-Class opponent. In this form, Vali can use one of Albion's lost techniques, a lethal poison that affects everyone except for Ddraig, Ophis, Wagyl, and Scarlet Grand. The time this form can be sustained is very limited. Its finishing move is the Divinity Apollo Driver.

Silver Dragonar Nekomata (シルバー・ねこまた・ドラゴナー, Shirubā Nekomata Doragonā):

Plate Mails
The Plate Mails are mindless mass produced puppet versions of the Boosted Pump and Divine Dividing Scale Mails created by Drakon La Leviathan to serve as Trihexa's subordinates. Trihexa was also modified in order to reproduce more of them as reinforcements.

Trivia

 * Scale Mail is the only Overdrive that can be used by more then one Ancient Gear.
 * Both the archdemon Cythraul and God Vidar have been able to create their own forms of Scale Mail armors through pacts with Dragons such as Apophis and Midgardsormr.
 * Cardinal Crimson Incursio is modeled after the ZGMF-X10A Freedom Gundam from Mobile Suit Gundam SEED.
 * Divine Dividing's White Scale Mail's Wings of Light bears a heavy resemblance to Lancelot Albion's Energy Wings from the Code Geass series.