Tachyon, with the best Turn 1 and Turn 2 in the meta (between its consistent boards with Loading... backup and immense OTK potential), finds itself debuting in a Tier 0 position.
Tachyon is simply insane, it came to break the game and makes all other decks (with the exception of Shiranui) look horrible by comparison. Furthermore, some cards that have never seen Main Deck play are now seeing use, like Loading... and Loading... , as they are the only way to try to combat the deck.
Tachyon has it all: twice per Duel Skill that searches a combo piece with a free summon while also searching Loading... (probably one of the best counter traps ever printed), ability to go second thanks to their extenders like Loading... , big beaters, one of the strongest Extra Deck toolbox in the game (Rank 8's) and practically no weakness to any Hand-Trap due to the lack of chokepoints.
The deck has dominated every tournament since release and some counters like Loading... and Loading... (If they end on Loading... however they can play around it) have popped up recently. That being said, without a proper counter, the deck will continue to dominate.
Tachyon, the deck that no one expected, is the perfect deck going first, thanks to the ability to easily end on Loading... , a Rank 8 monster, and Loading... . Going second, the deck just spams Rank 8s thanks to Loading... , making it incredibly powerful. If that weren't enough, the deck also has access to potent cards like Loading... and Loading... , which the deck can easily draw into with Loading... . This makes the deck seemingly unbeatable going first outside of the mirror. In our opinion, this dominance just make this deck Tier 0 and gives no reason to play any other deck if your goal is to win (as the deck has won practically all post-BOX tournaments).
In this age where going first makes the wealth of difference, the newly-arrived Tachyon deck has the least difficulty going second thanks to Tachyon Dragon Domination , their new broken skill. The most important difference between new Tier 0 Tachyon and the other decks is its going-second turns. When the deck summons its first Xyz, Loading... , the deck can then immediately counter the most dangerous threat with a searched Loading... , a Loading... -esque Counter Trap that can be activated from the hand. The deck is also able to easily summon 2 Rank 8 Xyz monsters in a single turn, making it a much more disruptive version of the old Galaxy-Eyes decks.
Personally, I'm not sure what Mayakashi has going for it going first or second against Tachyon. Its main tool in Loading... reviving Loading... can be easily extended through by Tachyon, and should Tachyon wait to Loading... a Synchro Monster's on-summon effect, Mayakashi's Synchro chain, vital to their survivability, gets cut off as the negated cards get shuffled back into the deck.