The matchmaking algorithm determines which opponents a player will fight in the upcoming stage. Half of the players will randomly be chosen to travel to an opponent’s board to fight in the upcoming turn. If there are an odd number of players remaining, a ghost will be generated to fight one of the remaining players.

Note: If two fully empty boards fight each other, the player that traveled to the board will receive the win.

Ghost - a copy of a surviving player’s board, chosen at random. The fight is the same as if the ghost is a player, except in the case of a tie in overtime. Ties do not result in player damage.

Simplified Explanation

In general, you can’t fight the last 4 people that you have fought. This number is reduced when players start to die later in the game, but you will never fight the same player twice, not counting ghosts.

Comprehensive Explanation

During stage 2, a queue of players is established, such that you will match against a new unplayed opponent for every pvp round during stage 2.

Starting at stage 3-1, there is a pool of 3 players at all times that you are eligible to match against. At 3-1, this consists of the first player you matched against, and the two players who you have not yet played. Out of this 3 person set, one will be randomly selected.

At the next stage, 3-2, the player who was just played is now moved to the back of the queue, and the player at the front of the queue is now added to the potential 3 player set. From here on out, the players in this constantly updated 3 player set are who you can face against during every turn.

Trackers

Riot has allowed for the use of 3rd party extensions to help track opponents, such as:
MetaTFT: https://www.metatft.com/download
Blitz.gg: https://blitz.gg