I am still in awe to this day that Konami has never made a catch-all term for Extra Deck Monsters.
Even the catch-all term for Main Deck monsters is the clunkiest fucking wording they've done and never touched again
>monster [...] that began the Duel in the Main Deck
Like holy shit just come up with a keyword or term for them. Even just "Extra Deck Monster" and "Main Deck Monster" works perfectly.