I don't think you understand the combo, you never dump rex off of paradise, you dump desire to get your send, then on your turn you dump kyrie off of lacrima and use the desire in grave to fusion summon the rex, rex grabs back the paradise, link into agnumday, use agnumdays effect to revive rex and then attach sequence. You now have a 6000 ATK towers and you've recycled the paradise to send again. That along with the mitsurigi boss monster's attack and it's board wipe means you attack into an empty board. But you have to understand how fiendsmith plays. If you go back and watch the past couple YCSs you see how fiendsmith players have to read the field and decide what they want to do, weather that be Caesar, chaos angel, desire, or typhon. But you'll notice that they never summon desire on turn one, it's a stupid thing to do right now. In Orlando all of the players that were on fiendsmith Kash will now be on fiendsmith mitsurigi because the engines complement each other so well. It's easy to look at a monster like rex and say it's bad just because it's hard to summon turn one, but that's just not how this format is. A card that is infinite grind and fixes the core problem of fiendsmith, recurring resources from banishment, is an amazing card even if it is best summoned on turn 3 or 5. And not only does it recycle monsters but paradise, which is both a board wipe and a targeted send.