Galaxies is bringing a complete overhaul of Teamfight Tactics, including new origins, new classes, new champions and also a brand new mechanic system to replace the Elemental Hexes: the Galaxies.
While we don't know a lot about this mechanic, it's supposed to transport us into different dimensions where rules apply differently. For instance, all players would start the game with one Neeko's Help, or the first Carousel would be filled with Tier 4 champions.
Riot Games is planning to add a lot more of theses Galaxies, but apparently we will have to wait until Patch 10.7 to discover all of them.
Via this tweet, we learn the existence of three new Galaxies:
The Trade Sector, a place where the first reroll of each round is free, the Superdense Galaxy, where players receive a free Force of Nature on reaching level 5, and the Not So Little Legends, where Little Legends have more starting health and are larger.
It remains to be seen what will be the other ones, but we will have to wait for Patch 10.7 — or even 10.8 — to know more about it.