Introduction of Ranked
Ranked is now included in Teamfight Tactics on PBE! At the end of every match, the top four players will gain ELO, while the bottom four will lose ELO. The current number of placement matches on the PBE is five matches before officially getting a rank.
As time goes on, hopefully we will have more information on what determines ELO gained. For example, once you have a steady rank established, one would imagine a loss of ELO to be different if you placed fifth rather than last place. In addition, it might make sense to have placing first carry more weight in promotional matches.