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"Krawler" is an archetype of Level/Link 2 EARTH Insect monsters (except the Level 9 "Deus X-Krawler") introduced in Circuit Break. The archetype is related to, and is supported by, the "World Legacy" archetype.
They appear to be based on "mob" enemies from RPGs that usually scour the game areas and frequently engage the player in combat, letting them gain experience and increase their stats.
- The Mystery of the "Krawlers" Connected to the "World Legacy" Draws Near!
We're unveiling the hidden story of the "Krawlers", one of the many mysterious new themes debuting in "Circuit Break".
- The Territory of the "Krawlers"
Mechanical lifeforms called the "Krawlers" multiply in the land where "World Legacy - "World Armor"" sleeps. With forms far too diverse to be called monomorphic lifeforms, it's believed they are the result of accelerated "adaptive radiation", i.e. the rapid diversification of organisms into different evolutionary forms. They exist as a super-organism that work in parallel with one another using a unique Neural Network, and no member of the "Krawlers" has their own sense of identity. In the past, some parts of the "Krawlers" became extremely violent, but though it's recorded they did attempt to invade the "Celestial Forest", it's uncertain why they did. If they lack an sense of self, what kind of 'will' is interfering with their behavioral principles to cause this?
- The Land Where The "World Armor" Lies
There is a Legacy, or Relic, of the "Celestial Deity" of the world, that lies in the center of the vast wetlands that are the territory of the "Krawlers". It is known as "World Legacy - "World Armor"". Although its exact connection with the "Krawlers" whose territory centers around the great vast wetlands is unknown at the moment, there are theories that the fact the "World Armor" exists is related directly to the "Krawlers" existing, and the creation of the wetlands themselves. It is known that the "World Armor" periodically and regularly has a dark light that emanates from it, and it seems individual "Krawlers" flicker at the same cycle as this light, but the details are unknown. At the same time the "World Chalice" came in contact with the girl "Crowned by the World Chalice" in the "Celestial Forest", the "Krawlers" began to swarm around the "World Armor". Twenty-four hours later, what "Auram the World Chalice Blademaster" and his friends saw before them once they arrived at the vast wetlands, guided by the "World Chalice", was the earth covered in the hordes of the "Krawlers", glowing with crimson lights.
- The Horde Covering The "World Armor"
The red-stained earth. A light that spelled danger glowed from the countless "Krawlers" swarmed around the "World Legacy - "World Armor"". The "Krawlers" linked to the "World Armor" via the Network, rapidly evolved further, and some even mutated into brand new species. These mutations caused "X-Krawlers" to form, one after another. The "Krawlers" expanded their Neural Network, which increasingly centered on the "X-Krawlers". Although the intentions of the "X-Krawlers", who continue to multiply at an accelerating rate, are unknown, they are protecting the "World Armor", and their behavior of eliminating intruders is already far beyond normal biological instinct, so there's no doubt they have hostile intentions.
- Those That Seek The "World Legacy"
"Auram the World Chalice Blademaster" and his friends were surrounded by the horde of "Krawlers", with the "X-Krawlers" at the heart of everything. "Auram" and "Imduk the World Chalice Dragon" were steadily cornered despite fighting as hard as possible. But things got better as "Lee the World Chalice Fairy" determined the weaknesses of the "Krawler" horde. Aiming for the "X-Krawlers" that had become their control towers, they managed to silence most of the "Krawler" swarm. Breaking through the hordes of "Krawlers", the three hurried towards their friends they had been cut off from during the fierce fight, but no one noticed the minor change that happened to "Lee".
- The Eerie Shadows Quietly Make Their Moves
Meanwhile, "Ningirsu the World Chalice Warrior" and "Ib the World Chalice Priestess", who got separated from "Auram" and the others, found themselves stuck in the midst of an rather large horde of "Krawlers". Believing that "Auram" and the others would come to help, "Ningirsu" fought hard to protect "Ib". However, shortly after reuniting with their comrades who finally arrived, "Ib" is caught by mysterious figures different from the enormous swarm of "Krawlers". Chasing after "Ib", who had been abducted, a new battle is about to begin for her and her friends. 
|Axon||Axon||Destroys a targeted Spell/Trap on the field when flipped.|
|Dendrite||Dendrite||Sends a monster from the controller's Deck to the GY when flipped.|
|Glial||Neuroglia||Special Summons a "Krawler" monster from the controller's hand or GY in Attack Position or face-down Defense Position, except "Glial", when flipped.|
|Ranvier||Ranvier||Adds up to 2 targeted "Krawler" monsters in the controller's GY to their hand when flipped.|
|Receptor||Receptor||Adds a "Krawler" monster from the controller's Deck to their hand when flipped.|
|Spine||Spine||Destroys a targeted monster on the field when flipped.|
|Deus||Deus ex machina||(effects are all different from the other members')|
|Neurogos||Neuron||Pointed "Krawler" monsters cannot be destroyed by battle, gain 300 ATK/DEF, and inflict doubled battle damage when they battle the opponent's monsters.|
|Qualiark||Qualia||Depending on the number of "Krawler" monsters controlled, the controller's monsters all gain 300 ATK/DEF (2+), the opponent cannot activate card and effects during the Battle Phase (4+), and the controller's monsters can all attack directly (6).|
|Synaphysis||Synapse||Pointed "Krawler" monsters cannot be destroyed by battle, gain 300 ATK/DEF, and can attack twice per Battle Phase.|
The "Krawler" archetype's main goal focuses upon using sheer numbers to overwhelm the opponent by swarming the field with as many of its monsters as possible. As the archetype is primarily comprised of Flip monsters, there is a focus in first getting them flipped face-up in order to trigger their Flip effects, putting them in a position to then accomplish said main goal. The archetype does this through effects possessed on all of its monsters whereby two "Krawler" monsters are Special Summoned when the monster is removed from the field due to an opponent's card effect, effectively doubling the controller's field presence as a result. As the monsters need to be face-up for the effect to activate and said effect Special Summons more "Krawler" monsters face-down, this provides an incentive for the controller to first flip them face-up in order to utilize the Flip effects, then have the opponent remove them with a card effect in order to make full use of both effects. In order to ensure that this shared effect can trigger, the archetype also has a secondary aim of restricting the opponent's moves by complicating their attempts to remove its monsters from the field through destruction by battle.
The archetype's Main Deck monsters are completely comprised of Flip monsters, each with two effects. The first effect is a Flip effect that is unique to the monster, and focus upon either advancing the player's resources or destroying cards on the field. The second effect is a common Trigger Effect that activates if they leave the field due to an opponent's card effect while face-up and controlled by their owner, enabling the controller to Special Summon 2 "Krawler" monsters with different names from their Deck in face-down Defense Position, with the exception of a monster that has the same name as the monster that left the field.
The archetype's Link Monsters, all being Link 2 and able to be Link Summoned using 2 members of the archetype, all share a common effect wherein if they leave the field by being destroyed by battle or due to an opponent's card effect while face-up, the controller can Special Summon 2 "Krawler" monsters from their GY in face-down Defense Position, once again increasing their field presence and enabling the controller to perform another Link Summon later on. This effect also forces the opponent into a position whereby any form of removal will trigger it, thus playing into the archetype's strategy of manipulating the opponent's removal options. The archetype's Link Monsters also possess unique effects that augment the battling capabilities of its monsters, making up for their low ATK and enabling the archetype to be a capable threat in battle.
"X-Krawler Neurogos" and "X-Krawler Synaphysis" share many common traits, namely that both possess Left and Right Link Arrows, and grant "Krawler" monsters linked to them 300 ATK and DEF, and indestructibility by battle. The latter trait is particularly useful for the archetype, as it further cuts off the opponent's options in removing the archetype's monsters by battle and forces them to use card effects, thus triggering the common effect of the Flip monsters. Additionally, "Neurogos" doubles the battle damage that "Krawler" monsters linked to it inflict upon the opponent, while "Synaphysis" enables "Krawler" monsters linked to it to make 2 attacks on the opponent's monsters during the Battle Phase, traits that further bolster the archetype's capability to inflict mass damage to the opponent in concert with its ability to swarm.
Due to the positioning of the Link Arrows for "Neurogos" and "Synaphysis", the controller can only take advantage of their linked effects while they are in Main Monster Zones. However, the controller can use this trait to their benefit, as for greater protection, copies of "Neurogos" and "Synaphysis" can be co-linked to each other, enabling them to mutually increase each others' ATK and protect each other from battle destruction, traits that they can bestow upon other "Krawler" Monsters, but not themselves.
While it possesses stronger unique effects than "Neurogos" or "Synaphysis", "X-Krawler Qualiark" is heavily dependent on the archetype's ability to swarm, as it applies its effects based on the number of "Krawler" monsters that the controller controls. However, like the unique effects of "Neurogos" and "Synaphysis", such effects provide potent boosts to the archetype's battling capacities. Should the controller control 2 or more "Krawler" monsters, the ATK and DEF of all monsters the player controls are bolstered by 300, similarly to the common effect of "Neurogos" and "Synaphysis". The controller controlling 4 or more "Krawler" monsters prohibits the opponent from activating cards and effects during the Battle Phase. Finally, if the controller controls 6 or more "Krawler" monsters, monsters they control can attack the opponent directly. Because "Qualiark" possesses Bottom-Left and Bottom-Right Link Arrows, it serves the archetype best if it occupies the controller's Extra Monster Zone, as in that role, it can act as an initiator for other Link Summons and facilitate the ideal placement of copies of "Neurogos" and "Synaphysis" in the Main Monster Zones, and by extension, the construction of a series of such monsters co-linked with each other in order to reap mutual benefits.
Given that the archetype is related to the "World Legacy" archetype, it also enjoys some support from that archetype's cards. The archetype's associated "World Legacy" monster, "World Legacy - "World Armor"" can be Special Summoned from the controller's hand when a monster is Flip Summoned, which can be easily enabled within the archetype. However, should it be Normal or Special Summoned, "World Armor" possesses an effect wherein the controller can search out a "World Legacy" card from their Deck to add to their hand, providing the controller with a way to search out support for either its archetype or the "World Legacy" cards connected to the "Krawler" archetype. Additionally, if it was Normal Summoned or Set, "World Armor" also has a Quick Effect that allows the controller to return both itself and a face-up monster controlled by the opponent that was Special Summoned from the Extra Deck to the hand, allowing for the removal of such monsters that may threaten the controller's efforts to build a field with "Krawler" monsters. Despite "World Armor" being a Level 7 monster, it can easily be Normal Summoned or Set in a "Krawler" deck, as the archetype provides ample Tributes for it due to its common effects. Due to its high ATK and DEF, "World Armor" also allows the archetype a way to cover for the fact that its own monsters tend to be lacking in those stats.
The archetype's associated "World Legacy" Field Spell, "World Legacy in Shadow" has an shared effect with other "World Legacy" Field Spells in that it bolsters the ATK and DEF of the associated archetype's monsters by 300. Additionally, "Shadow" has two unique effects, the first being that it allows the controller to Special Summon a Level 2 or lower Insect monster from their hand in face-up or face-down Defense Position, giving the archetype a more reliable way to amass field presence either to initiate their swarming capabilities or gather monsters to use as Link Materials for a Link Summon. The second unique effect of "Shadow" triggers in response when the controller's Flip monster is destroyed by battle by an opponent's monster, allowing the controller to send that opponent's monster to the GY, which serves as a way to further dissuade the opponent from attacking "Krawler" Flip monsters and preventing their common effects from triggering. Because the opponent might be more weary of attacking Set monsters as a result of this effect, it also allows the controller a greater opportunity to Flip Summon the archetype's monsters themselves, providing a more reliable way to Special Summon "World Armor" via its Summoning condition.
In a pinch, "World Legacy Pawns" allows the controller a quick way to trigger the Flip effects of the archetype's Flip monsters, as it possesses an effect that can change a face-down monster the controller controls to face-up Attack or Defense Position. This is particularly useful if the opponent attempts to remove the controller's face-down "Krawler" monsters with card effects, as this effect will ensure that such monsters are face-up instead when they leave the field and can thus activate their common effects. "Pawns" also has another effect whereby the controller can return a "Krawler" monster from their GY to their Deck to flip a face-up monster they control face-down. Such an effect alleviates the fact that the archetype can potentially thin the Deck very quickly, especially if the controller is successful in consistently utilizing the common effects of the Flip monsters, while also enabling the controller to re-use the Flip effect of a "Krawler" monster.
Due to the archetype largely consisting of Flip monsters, "Book of Eclipse", "Book of Moon", and "Book of Taiyou" can be used to great effect to trigger their Flip effects or Set them face-down again. As the archetype is reliant on Link Summoning its Link Monsters as quickly as possible in order to enable that its Flip monsters are reliably protected from battle destruction, cards such as "Multiplication of Ants", "Worm Bait", and "Spider Egg" can help in Special Summoning Token monsters to use as Link Materials, making up for the fact that the archetype can be slower to initiate its swarming capacity compared to other archetypes. If the controller is unable to dissuade the opponent from destroying "Krawler" Flip monsters by battle, "Verdant Sanctuary" can be a viable option in order to prevent the controller from losing card advantage should their monsters be destroyed, though it can also be used in concert with the common effects of the "Krawler" Flip and Link Monsters as well.
Due to the tendency of the archetype's Flip monsters to be sent to the GY either because they were flipped face-up and destroyed by battle, or because their common effects were triggered, it is easy for them to accumulate such monsters in the GY. "Aztekipede, the Worm Warrior" and "Doom Dozer" can turn such cards into a utilizable resource by banishing them to facilitate their Special Summons. The latter also provides the Deck with a strong attacker to make up for most of the archetype's monsters having low ATK. The fact that the archetype's Flip monsters have low ATK and DEF can also be capitalized upon by including "Danipon", "Gokipon", and "Howling Insect" to the Deck, as all of them can be Set and easily destroyed by battle to search out the archetype's Flip monsters, with the latter two cards being able to search out any of those monsters. The first two cards are also Level 2, allowing for synergy with "Shadow" or "Verdant Sanctuary". "All-Out Attacks" is a useful option for the Deck in order to trigger the Flip effects of the archetype's monsters, by forcing the opponent to attack them. It can also be used in conjunction with "Shadow" to send the newly Summoned monsters to the GY, further disrupting the opponent's attempt to gain advantage.