Card evolutions

Retrained is the term used to describe a monster that has been reprinted with a new effect and slightly different name, but with the same base ATK and DEF, and usually Level as well. Examples include "Battle Ox" to "Enraged Battle Ox" and "Magician of Black Chaos" to "Dark Magician of Chaos". Special cases are Harpie Lady 1, Harpie Lady 2, and Harpie Lady 3, which all have the same stats as the original Harpie Lady, but are not all representing the same creature. Rather, they are the three sisters from Harpie Lady Sisters.

The term "retrained" comes from "Retrained Elf Swordsman," a translation of the Japanese name for "Obnoxious Celtic Guard", who is a retrained version of "Elf Swordsman" ("Celtic Guardian").

Retrained monsters are not to be confused with upgraded ones, such as Cannon Soldier MK-2. These, like retrained monsters, are clearly based on existing cards. However, unlike retrained versions, these have higher ATK and/or DEF and an effect meant to improve upon the original.

Retrained Cards

 * Battle Ox -> Enraged Battle Ox
 * Magician of Black Chaos -> Dark Magician of Chaos
 * Black Luster Soldier -> Black Luster Soldier - Envoy of the Beginning
 * Celtic Guardian -> Obnoxious Celtic Guard
 * Doll of Demise -> Malice Doll of Demise
 * Gaia the Fierce Knight -> Swift Gaia the Fierce Knight
 * St. Joan -> Guardian Angel Joan
 * Summoned Skull -> Skull Archfiend of Lightning
 * Swordsman of Landstar -> Swordsman of the United Landstars

Alternate Cards

 * Key Mace + Key Mace #2
 * Lava Battleguard + Swamp Battleguard
 * Level Limit - Area B + Level Limit - Area A
 * Crawling Dragon 2 + Crawling Dragon + Dragon Zombie

Monster Cards

 * Amphibious Bugroth -> Amphibious Bugroth MK-3
 * Cannon Soldier -> Cannon Soldier MK-2
 * Proto-Cyber Dragon -> Cyber Dragon -> Cyber Twin Dragon -> Cyber End Dragon -> Chimeratech Overdragon
 * Goblin Attack Force -> Goblin Elite Attack Force
 * Hane-Hane -> Hade-Hane
 * Man-Eater Bug -> Nobleman-Eater Bug
 * Muka Muka -> Enraged Muka Muka
 * Airknight Parshath -> Neo-Parshath, the Sky Paladin
 * Flying Fish -> Golden Flying Fish

Spell Cards

 * Umi -> A Legendary Ocean

Monster Cards

 * Black Luster Soldier - Envoy of the Beginning -> Sky Scourge Enrise / Ruin, Queen of Oblivion
 * Chaos Emperor Dragon - Envoy of the End -> Judgment Dragon -> Sky Scourge Norleras / Demise, King of Armageddon

Spell Cards

 * Change of Heart -> Brain Control -> Mind Control
 * Harpie's Feather Duster -> Heavy Storm -> Giant Trunade
 * Monster Reborn -> Monster Reincarnation
 * Mystical Space Typhoon -> Twister -> Tornado
 * Pot of Greed -> Pot of Avarice/Cup of Ace
 * Raigeki -> Lightning Vortex
 * Creature Swap -> Creature Seizure

Trap Cards

 * Mirror Force -> Dark Mirror Force -> Radiant Mirror Force

Transformed Cards

 * Airknight Parshath -> Darknight Parshath
 * Airknight Parshath -> Neo-Parshath, the Sky Paladin
 * Aqua Madoor -> Neo Aqua Madoor
 * Armed Dragon LV7 -> Dark Armed Dragon
 * Dark Magician -> Dark Sage
 * Dark Magician -> Dark Eradicator Warlock
 * Dark Magician -> Dark Magician Knight
 * Freed the Brave Wanderer -> Freed the Matchless General -> Dark General Freed
 * Gigobyte -> Gagagigo -> Giga Gagagigo -> Gogiga Gagagigo
 * Hand of Nephthys -> Sacred Phoenix of Nephthys -> Dark Nephthys
 * Harpie's Pet Baby Dragon -> Harpie's Pet Dragon
 * Helios - The Primordial Sun -> Helios Duo Megistus -> Helios Tris Megistus
 * Horus the Black Flame Dragon LV8 -> Dark Horus
 * Inpachi -> Blazing Inpachi -> Charcoal Inpachi -> Woodborg Inpachi
 * Levia-Dragon - Daedalus -> Ocean Dragon Lord - Neo-Daedalus
 * Machine King Prototype -> Machine King -> Perfect Machine King
 * Outstanding Dog Marron -> Mad Dog of Darkness
 * Outstanding Dog Marron -> Mecha-Dog Marron
 * Outstanding Dog Marron -> Skull Dog Marron
 * Petit Moth -> Larvae Moth -> Great Moth -> Perfectly Ultimate Great Moth
 * Rainbow Dragon -> Rainbow Dark Dragon
 * Red-Eyes B. Chick -> Red-Eyes B. Dragon -> Red-Eyes Darkness Dragon -> Red-Eyes Darkness Metal Dragon
 * Simorgh, Bird of Divinity -> Simorgh, Bird of Ancestry -> Dark Simorgh
 * The Creator Incarnate -> The Creator -> The Dark Creator
 * Thousand Needles -> Two Thousand Needles
 * Vampire Lord -> Vampire Genesis
 * Warrior Dai Grepher -> Dark Grepher
 * Warrior Lady of the Wasteland -> D.D. Warrior Lady
 * Warrior of Zera -> Archlord Zerato -> Darklord Zerato
 * Warrior of Zera -> Mazera DeVille
 * Warrior of Zera -> Zera the Mant
 * Yubel -> Yubel - Terror Incarnate -> Yubel - The Ultimate Nightmare

LV

 * Allure Queen LV3 -> Allure Queen LV5 -> Allure Queen LV7
 * Armed Dragon LV3 -> Armed Dragon LV5 -> Armed Dragon LV7 -> Armed Dragon LV10
 * Dark Lucius LV4 -> Dark Lucius LV6 -> Dark Lucius LV8
 * Dark Mimic LV1 -> Dark Mimic LV3
 * Horus the Black Flame Dragon LV4 -> Horus the Black Flame Dragon LV6 -> Horus the Black Flame Dragon LV8
 * Mystic Swordsman LV2 -> Mystic Swordsman LV4 -> Mystic Swordsman LV6
 * Silent Magician LV4 -> Silent Magician LV8
 * Silent Swordsman LV3 -> Silent Swordsman LV5 -> Silent Swordsman LV7
 * Ultimate Insect LV1 -> Ultimate Insect LV3 -> Ultimate Insect LV5 -> Ultimate Insect LV7
 * Winged Kuriboh -> Winged Kuriboh LV9
 * Winged Kuriboh -> Winged Kuriboh LV10

Metalmorph

 * Red-Eyes B. Chick -> Red-Eyes B. Dragon -> Red-Eyes Black Metal Dragon
 * Zoa -> Metalzoa
 * Musician King -> Heavy Metal King
 * Red-Eyes Darkness Dragon -> Red-Eyes Darkness Metal Dragon

Toon Monsters

 * Ancient Gear Golem -> Toon Ancient Gear Golem
 * Blue-Eyes White Dragon -> Blue-Eyes Toon Dragon
 * Cannon Soldier -> Toon Cannon Soldier
 * Dark Magician Girl -> Toon Dark Magician Girl
 * Gemini Elf -> Toon Gemini Elf
 * Goblin Attack Force -> Toon Goblin Attack Force
 * Masked Sorcerer -> Toon Masked Sorcerer
 * Summoned Skull -> Toon Summoned Skull
 * Red Archery Girl -> Toon Mermaid
 * Ryu-Ran -> Manga Ryu-Ran

Zombie

 * 3-Hump Lacooda -> Des Lacooda
 * Crass Clown -> Clown Zombie
 * Crawling Dragon -> Dragon Zombie
 * Zanki -> Armored Zombie
 * Red-Eyes Darkness Dragon -> Red-Eyes Zombie Dragon
 * Paladin of White Dragon -> Black Knight of Dark Dragon
 * Majestic Mech - Ohka -> Darkness Gear - Gokuen
 * Dark Ruler Ha Des -> Resurrection of Dark Ruler Ha Des
 * Chthonian Emperor Dragon -> Deathkaiser Dragon