Notes & Combos
tbh, I think that only a few decks really have the utility of Seventh Tachyon.
My reasoning is this: Do you have a circular-like that you absolutely want to have in hand to play? If yes: play it. Otherwise, it's a -1 card, and if you weren't playing Small World before, Tachyon is only barely better.
But in Exo, it's a different thing.
The deck has a lot of cards you'd rather avoid having in your hand (Irene, Extra Elis, etc.). Having the ability to return these cards to the deck improves the grind game, the use of Vadis, but also inevitably the consistency. She also turn our bad normal summons into good ones, like Sophia, who can allow you to draw the card you returned to the top of the deck via Tachyon, which removes the cost (I hesitated to play it x2 but lack of space). I'm waiting for Gem-Knight to arrive, because Nepyrim is basically a searchable one card combo (and which doesn't lock under purge), it seems promising to me.