I just noticed this topic and thought I'd correct you on something. A combo is technically any combination of cards used to make a move. Some people do make this mistake because they see a combo as something to win the game or do something big. Combos can come in big or small. So even moves like the Future Fusion + Dragon's Mirror can be considered a combo because they are a "combination" of cards used to make a move. It is definitely not as clever as Jowgen and Last Turn, but it is a combo none-the-less.
From yugioh.wikia.com
A Combo is a combination of 2 or more cards whose effects activate in such an order that allows the result to be different (and potentially more useful) than what would otherwise be normally possible. A common combination is "Book of Moon" combined with "Nobleman of Crossout" (which would allow a face down monster to be removed from play, which would not have normally happened because Book of Moon does not remove monsters from play and Nobleman of Crossout wouldn't have had a proper target to select first).
Although the end result of Future Fusion and Dragon's Mirror is still a Fusion, it is still slightly different than either card can provide because you're immediately Fusion Summoning a monster when you don't have all of the material monsters in your hand, field, or grave. Also, even though the monsters are removed from play by Dragon's Mirror, Future Fusion will still be able to Fusion Summon a second Fusion Monster.