Magician's Force (MFC) was the first set to contain Union monsters (which have the ability to combine with and strengthen other monsters,) as well as plenty of Spellcaster type monsters and Spellcaster-support cards. It is also the first set to contain the archetype of "Amazoness" monsters. In addition to new monster archetypes it introduced the "Spell Counter" mechanic in which certain cards could only be played by removing a number of "spell counters." This set is also noted for being the first set to mark the change of Magic cards to Spell cards. Highly sought after cards include Dark Magician Girl, Breaker the Magical Warrior, Tribe-Infecting Virus, Magical Scientist and Chaos Command Magician.