A "Mirror Match" is a match played between two people whose Decks are nearly identical, use cards from the same Archetypes or focus on roughly the same strategy. In Yu-Gi-Oh! Duelists of the Roses and Yu-Gi-Oh! Forbidden Memories, Deck Master K uses a Deck identical to yours as well.
A first example would be two Duelists using an identical/nearly identical Deck, like when Yugi and Yami Yugi dueled in Episode 163 (where the only card that made a difference between both Duelists' Decks was "The Seal of Orichalcos").
- Both Special Summoned their Normal, 2500 ATK ace monsters early on from their hand (Yugi's "Dark Magician" and Jaden's "Elemental Hero Neos").
- Both showed a monster-specific support card (Yugi's "Thousand Knives" and Jaden's "Spark Blaster").
- Their ace monsters attacked and destroyed each other, signifying equality.
- Both Summoned a Level 4 Normal Monster and attacked with it (Yugi's "Alpha The Magnet Warrior" and Jaden's "Elemental Hero Sparkman").
- Both used special effects to Normal Summon a high-Level monster without Tributes (Yugi's "Swift Gaia the Fierce Knight" by using its own effect, and Jaden's "Elemental Hero Bladedge" by using the effect of "Elemental Hero Necroshade").
- Both sent cards from their Decks to their Graveyards for effects that activate in the Graveyard (Yugi's "Archfiend of Gilfer" and Jaden's "Necro Gardna").
A third example would be two Duelists focusing on the same concept while using different cards, such as both players using the "Exodia" set while using different draw engines, or both focusing on burn effects while using different burn engines.
A fourth example would be using cards from the same archetype differently, such as one player using the material-specific "Elemental HERO" Fusions ("Shining Flare"/"Flame Wingman", "Rampart Blaster", "Thunder Giant", etc.) and one player using the "Omni Hero" (unofficial term) Fusions ("Absolute Zero", "Nova Master", 'The Shining", etc.), in which case both would have relatively the same Main Decks but different Extra Decks.