Dual Blades Overview

Dual Blades (双剣 Souken), or 'DB' (previously known as Dual Swords or 'DS') are a high speed class of weapon introduced in the western version of Monster Hunter (Not released in Japan until Monster hunter G). Their small attack stat and inability to block is made up for by their high attack speed and wide variance in elemental damage and status effects - some Monster Hunter games even allowing them to possess 2 different status effects simultaneously. Dual Blades can also increase their damage output via the "Devil's Dance" skill (akin to the Longsword's "spirit blade"), which increases damage output and does not cancel or overlap the effects of buff items (e.g. 'Demondrug').

Dual Blades are most notable for their "chain-attack" method of dealing large amounts of damage over time. This differs from Sword and Shield methods of creating grandiose combos or infinite strikes (as opposed to short combos which move the player dramatically). 

- Weapon Traits :

Dual Blades are more than just a couple of blades to slash and maim:

• Dual Blades do not provide shielding ability, but can roll after an attack, though rolling is not possible in the middle of a combo.
• Dual Blades' combos can do very high damage over time.
• Some attacks on Dual Blades are one sided, for example, pressing "circle" will do a quick spin-slash upwards to the right side, but if you press circle as well as left on the analog stick, your slash will be left-upward.
• Because they are quick to deal multiple strikes in a short amount of time, Dual Blades lose sharpness faster than other weapons. Also, when dual blades reach below standard sharpness the Demon's Dance will not complete and will only have 4 or 5 hits. Always carry spare Whetstones when using Dual Blades.
• Elemental damage dealt with Duals is 30% less than what is shown. However, it is a very excellent weapon when it has elements.
• If you land an affinity hit on the first hit of every input combo, the rest of the hits will all be affinity hits.
• While wielding Dual Blades, you can enter Demonization mode, this mode allows you strike faster, deal more damage, and resist Wind Pressure and have super armor on non-boss attacks. While in this mode, hitting triangle and circle at the same time will initiate a combo, called the Demon's Dance, that will not bounce on contact.
  • Demonization has a big drawback however. While in this mode, your stamina will drain at a quick pace until it is completely drained or Demonization is ended manually. Demonization also limits chances to dodge because when it ends, hunters are often left with no stamina to dodge with. This can be prevented with Power Juice, Mega Juice, or Mopeshroom if equipped with Mushroom Lover or Power Eater armor effects.
  • Demonization mode can be ended manually by re-pressing R or sheathing your weapons.
• Each sword can have different elements. For example, the weapon Snow Venom  wields both poison and ice elements. 

- Changes in Gen 3 and up

Like the Hunting Horn, Dual Blades receive significant revamps in P3rd and 3U. Replacing "Demonization" is a new system aided by the "Demon Gauge," which is displayed under the sharpness bar. Movement animations also differ greatly from previous series. The changes are as follows:

• The new system involves three fighting states for the user: Normal, Demon and Archdemon mode.
• The normal mode is the usual state of the user without any special buffs. This mode is reminiscent of the previous series with some exceptions:
  • The normal combo animation is altered into a faster and more aggressive one with wider time frame for evasion.
  • The spinning attack combo, instead of simply spinning once in chosen direction, will be started with a very quick "Jab'n'Slash" that will link directly to the spinning attack on the second button press.
• The Demon mode is the "Demonization" which, like the original, can be activated by pressing the "Special Act" button of the console with the weapon drawn. Attack animations are altered and the ever-famous "Demon Dance" is added, but stamina is constantly drained while this mode is active. Effects include:
  • The primary combo in 3rd gen is drastically different in this mode and actually lands less hit while sacrificing mobility of the user.
  • The "Jab'n'Slash" attack is absent, replaced instead by the classic double spin attack.
  • The roll is replaced with "Demon Dodge", an advanced evasive maneuver where users "strafe" into chosen direction. This "dodge" can link to attacks instantly and has a surprisingly moderate invulnerability time-frame. However, it still drains stamina, which when coupled with the Demon mode's constant stamina drain, severely depletes the stamina gauge. It also does not cure Fireblight and Slimeblight/Blastblight.
  • Landing hits in this mode will fill up the "Demon Gauge," which is needed to activate and utilize the "Archdemon Mode".
• The Archdemon mode is a mode that a Dual Blades wielder should try to maintain during battle. To enter this mode, one must exit Demon mode after the gauge is full. The mode combines the best attack animations from the other two modes and changes the normal dodge into demon dodge. Any offensive or evasive actions while the weapon is drawn will deplete the gauge. If the gauge runs out completely, Archdemon mode will end. Idling will also cause the gauge to deplete.
  • The mode takes the primary combo of Normal mode and can be linked into the later half of Demon Dance moves.
  • The spinning attack starts with "Jab'n'Slash" and can be linked to a Double Spin.
   

- Pros and Cons :

  
Advantages

• Dual Blades have a myriad of improvements at the Weapons and Equipment shop. They can also be upgraded with different attributes to immensely strengthen their wielder.
• Demonization allows a wielder to unleash destructive attacks that will crush almost any opponent.
• Dual Blades will still continue dealing attribute attack even if Sharpness decreases.
• Can stack a lot of damage in a short amount of time.
• Fast sheathing.

Disadvantages

• Sharpness drops quickly with Dual Blades.
• No guard ability.
• Stamina decreases fast with Demonization, requiring Dash Juice to sustain a wielder.
• Low damage (speedy attacks and long combos can make up for this).
• Smallest range out of all weapons, requiring uses to be much closer to the enemy and thus increasing their risk of getting hit. Additionally it makes it difficult for them to hit flying enemies or large bosses with body parts that hang overhead and out of reach.
• Awkward evasion capabilities — hunters may sometimes find themselves "locked" into a stream of attacks and unable to dodge when they need to. Additionally, their roll and Demon Dash covers a short range (with Demon Dash being much shorter than their roll), making it difficult to escape from attacks with large hitboxes, especially when they linger for very long. 

- Tutorial for Beginner Hunter (by GaijinHunter / @aevanko) 

https://www.youtube.com/watch?v=CQv_qrL7no4