Last week saw the second-to-last card of the Duelists of Brilliance pack being revealed and despite only being one card revealed by Twitter post, it's an extremely versatile card!
Seventh Tachyon is essentially a searcher that can get you a monster by revealing any of the Numbers between 101 and 107, letting you fetch anything on the same axis and the same Type and/or Attribute. You're locked out of anything except Xyz Monsters from that point but that's a necessary restriction because this searches downwards of 2,792 cards.
Every Level 4 monster that's FIRE, WATER, EARTH, or LIGHT is searchable by this. Every Level 5 that's one of those Attributes or DARK is searchable by this. Every Level 4 or 5 that's Aqua, Fairy, Spellcaster, Warrior, or Rock is searchable by this. Level 8 LIGHTs and Dragons are searchable by this. Even Level 9s that are LIGHT or Dragons are searchable by this.
Even if it's only really useful in Xyz decks or decks that don't use their Extra Deck, it's still a powerful search tool that - bonus - you can actually search off another card, Seventh Ascension.