This set introduced pendulum monsters, a series of cards that can be used either as monster cards or spell cards and can help swarm the field through the pendulum summon mechanic
Duelist Alliance
Orcust
Orcustrated Return
(2 answers required)
Dogmatika Ecclesia, the Virtuous/Fallen of Albaz
Yang Zing
Nine Pillars of Yang Zing
As if burning wasn't enough, this card is also capable of wiping a board in large enough numbers and fired from an actual cannon
Volcanic Scattershot
Avram's swords were originally carried by this monster
Mekk-Knight Blue Sky
"This set introduced the Qliphort archetype, a series of machine pendulum monsters capable of swarming the field while being immune to most monster effects."
The New Challengers
Lightsworn
Solar Recharge
Grandmaster of the Six Samurai
Gravekeeper
Imperial Tombs of Necrovalley
This card was known in old formats for spot banishing removal, but could also burn if you hit the right card.
Caius the Shadow Monarch
After the activation of the World Wand, World Legacy - World Lance took on the form of this monster
Guardragon Agarpain
This set introduced the Gladiator Beasts, an archetype that focuses on battling, then tagging out by shuffling themselves into the deck after doing so and tutoring one another from the deck
Gladiator's Assault
Red-Eyes
Cards of the Red Stone
Exa, Enforcer of the Nekroz
Magikey
Magikey Unlocking
A classic DM card known for its role in old burn FTKs, this card received an errata in 2014
Catapult Turtle
This is Chosen by the World Chalice's first upgraded form
Auram, the World Chalice Blademaster
This set introduced the Six Samurai, an archetype of warriors that revolve around swarming the field in an attempt to gain an advantage over the opponent
Strike of Neos
Tenyi
Flawless Perfection of the Tenyi
3 answers required
True King of All Calamities/Metaltron XII, The True Dracocombatant/Master Peace, The True Dracoslaying King
Venom
Snake Deity's Command
Destiny End Dragoon
The core of this monster found itself in Knightmare Unicorn
Mekk-Knight Yellow Star
This was the first set to release an actual archetype into the game: Gravekeepers'
Meklord
Boon of the Meklord Emperor
2 answers required
El Shaddoll Wendigo/ Pilica, Descendant of Gusto
Solfachord
Solfachord Formal
Originally released as a Shonen Jump promo, this monster further punishes opponents after their stuff gets negated by your counter traps.
Van'Dalgyon the Dark Dragon Lord
This monster's name is based on a computer program based on the original Tierra program, designed to simulate life
Avida, Rebuilder of Worlds.