Card evolutions

Retrained is the term used to describe when a monster is reprinted with an new or improved effect. examples include Battle Ox to Enraged Battle Ox and Magician of Black Chaos to Dark Magician of Chaos. Other cards that fit into this catagory are listed below:

• Black Luster Soldier to Black Luster Soldier - Envoy of the Beginning
• Gaia the Fierce Knight to Swift Gaia the Fierce Knight
• Celtic Guardian to Obnoxious Celtic Guard
• Summoned Skull to Skull Archfiend of Lightning

Trivia:

• The term "retrained" comes from "Retrained Elf Swordsman," the Japanese name for Obnoxious Celtic Guard.