The "lswarm" crest.
"lswarm", known as "Verz" (ヴェルズ Veruzu) in the OCG, is a Duel Terminal archetype of DARK monsters which was introduced in Duel Terminal - Sacred Star Knights!!. Despite being released prior to "lswarm", the "Steelswarm" archetype is an "lswarm" sub-archetype, thus all "Steelswarm" monsters are supported by "lswarm" support cards. "Evilswarm Exciton Knight" and "Steelswarm Origin" are the only non-DARK members (being LIGHT instead).
The most significant feature of the non-"Steelswarm" "lswarm", except "Evilswarm Kerykeion" and "Evilswarm Exciton Knight", is that their ATK/DEF end with 50, and all known "lswarm", except "Evilswarm Golem", "Evilswarm Coppelia" and "Steelswarm Origin" are Level or Rank 4.
Both "Steelswarm Caucastag" and "Steelswarm Moth" appears as characters in Yu-Gi-Oh! 5D's World Championship 2011: Over the Nexus, and "Evilswarm Ouroboros" appears in Yu-Gi-Oh! Duel Arena.
Each non-"Steelswarm" "lswarm" is based on a member of a previous Duel Terminal archetype, corrupted by the "lswarm" virus that was released from "Steelswarm Cell", shown in "Infestation Infection". There is an "lswarm" counterpart for each Duel Terminal archetype except "Vylon".
A crisis has struck the Duel Terminal world. Nearly all living things across the planet have been corrupted, their bodies warped, and their minds slowly seized by a desire to destroy that is so strong, it becomes impossible to interact with others. The elders of the planet linked it to ancient lore of an identical plague, and so dubbed the infection, and the infected, the "Evilswarm".
"Inverz" could be seen as a shortened version of "Insect Verz" or "Insectoid Verz", meaning the "Verz" virus might have come long before the "Steelswarm" did, and the "Steelswarms" are a heavily-infected species of creature. Even the "lswarm" symbol can be seen as an outline of "Steelswarm" symbol (best seen on the horse of "Evilswarm Thanatos").
Another possible theory is that the "lswarm" virus is a defense mechanism the "Steelswarm" implement upon extinction that works to reconstruct their race. This can be seen by the goal of the "lswarm" controlled "Gishki Noellia" being to resurrect "Steelswarm Hercules", the overlord of the "Steelswarm".
It is also possible that with the destruction of the "Steelswarm" at the hands of the "Vylon", the virus then could have corrupted or even copied the other Duel Terminal archetypes.
In addition, "Ver" is French for "Worm". This may signify that their role is similar to the "Worms" in the previous Duel Terminal story as the first, horror movie-like antagonist ("Worms" being aliens, "lswarm" being the zombie virus), followed by a holy/unholy antagonist that at first appeared to be an ally ("Fabled" and "Vylon"). More parallels can be drawn, for example Las Plagas the parasitic-organism featured in both Resident Evil 4 and 5 were buried underground by a Spanish Castellan, while the "lswarms", the carriers of the "Evilswarm Virus", were sealed underground after losing against the "Vylon", also both of them can equally corrupt their hosts while making them stronger.
The non-"Steelswarm" "lswarm"s is a sub-archetype that focuses on Summoning Rank 4 "Evilswarm" Xyz Monsters using "Evilswarm Castor", "Evilswarm Mandragora" and "Kerykeion" to swarm Level 4 "Evilswarms". The "Evilswarm" Xyz Monsters are very powerful: they add field control to the Deck with "Evilswarm Ophion", which prevents the Special Summon of any Level 5 or higher monsters, shutting down many popular Decks such as "Agents" and "Chaos Dragons", "Evilswarm Nightmare", which disrupts Special Summoned monsters, and "Evilswarm Bahamut", which can permanently take control of your opponent's monster for a cost. "Evilswarm Ouroboros" can be used to gain hand and field advantage and by banishing a monster from the opponent's Graveyard (disrupting cards like "Grapha, Dragon Lord of Dark World" or "Steelswarm Scout"/"Treeborn Frog").
"lswarm" Decks can also potentially utilise "Chaos Zone" effectively, as "Evilswarm Salamandra" and "Evilswarm Thunderbird" provide large amounts of counters (repeatably) and are useful in their own right. An "lswarm" Deck using "Chaos Zone" can also benefit greatly from "Creeping Darkness", as it adds the core type of monster, Level 4 DARK, as well as 2 "Chaos Counters", making the re-Summoning of the monsters used for the cost relatively easy. "Allure of Darkness" can also be very useful in this type of Deck, with its negative effect partially offset. The latest "lswarm" monster, "Evilswarm Kerykeion", works particularly well in a "Chaos Zone"/"Xyz" Deck by recycling a monster as well as adding an extra Summon and a "Chaos Counter". Some might say that 3 copies can replace some or even all copies of "Evilswarm Castor", "Evilswarm Salamandra" and "Creeping Darkness".
"Dark Armed Dragon" is a relatively easy card to Summon in an "lswarm" Deck, with its high level of Graveyard manipulation through Xyz costs and "Evilswarm Salamandra"/"Creeping Darkness"/"Evilswarm Kerykeion" and large proportion of DARK monsters.
Whether or not to use the higher Level cards like "Evilswarm Golem" or "Evilswarm Coppelia" is a matter of personal preference, as they are powerful cards but are not useful for Xyz Summoning. Also, "Golem" is low in ATK, making it almost useless against another "DARK" Deck. However, it may be a good idea to place "Golem" in a Side Deck in a tournament to deal with Decks like "Naturia" or a particularly strong non-DARK key card, such as "Master Hyperion".
A recent development is a version of the basic non-"Steelswarm" "lswarm" Deck using "Evilswarm Heliotrope", "Evilswarm Castor", "Evilswarm Kerykeion", "Evilswarm Mandragora" and "Rescue Rabbit" as the only monsters in the Main Deck. The rest of this Deck is given over to protection cards such as "Forbidden Lance", "Dark Illusion" and "Infestation Pandemic"; This type of Deck uses "Evilswarm Ophion's" effect to block opponents' Summoning their strongest cards while keeping it on the field through the strong control elements in the Deck, eventually using up its "Xyz Material"s on the turn a replacement is Summoned. In a way, this type of Deck could be compared to "Dino Rabbit" decks, given its propensity for high-ATK Level 4 monsters and continuous use of disruptive effects.
- First, as all "Evilswarms" are DARK-Attribute, the "Koa'ki Meiru" series and cards like "Shadow-Imprisoning Mirror" or "Consecrated Light" can potentially disrupt these monsters.
- The effectiveness of an "Evilswarm" Deck is heavily dependent on the current metagame; "Evilswarm Ophion" can easily shut down Fusion, Synchro, Ritual, and some Pendulum-focused Decks, but is often useless against most Xyz, Link, and Tribute Summoning-based Decks.
- Cards like "Skill Drain", "Angel O7" and even "Forbidden Chalice" can negate their effects on the Field.
- One of the most devastating fields to watch out for is "Mystical Fairy Elfuria" backed by tons of Spells and Traps or other protection. If they continue to reveal anything other than a Level 4 monster in hand, they can potentially shut down your deck's entire arsenal.
- Decks that do not rely on high-level monsters and can bring out monsters that can easily dispatch "Evilswarm" monsters are also a weakness to the Deck, such as "Constellars", who can easily bring out a turn-one "Constellar Pleiades" or "Starliege Paladynamo" and easily eliminate any of your monsters with ease.
- A common Side-Deck card is "Genex Ally Duradark", because of its ability to easily destroy any monster in the "Evilswarm" archetype, provided they are in Attack Position.
- As most "Evilswarms" are different types a common Side Deck card against them is "Rivalry of Warlords"; this prevents players from going into an Xyz Monster that has a different Type than the monster(s) they control.
- "Castor" and "Pollux" are separate monsters and are brothers in the Duel Terminal storyline. The former was infected by the "lswarm" virus, not the latter. The original form of "Castor" is depicted in "Constellar Meteor".