We've been collectively referring to those players "voted off the island" as some variation on the following:
What we haven't really done in much detail thus far is to map out exactly what the role of the player who finished with the worst record of a four-person team can do. In the interests of keeping the tournament fair and fun, a clear set of guidelines has been produced to make sure the fourth players can participate in their own way, without creating their own set of rules issues.
The central idea of these rules is to remind everyone that the fourth player does still count as a player on the team, rather than some sort of Wild West figure able to go scout around and get players information or advantages they shouldn't otherwise have. All tournament policies still apply to them, meaning that things like outside notes are still not allowed during games. For full clarity, here's a list of what the fourth players can and can't do.
During Team Sealed Build
The fourth players must be with their teams from the start of the deck build, and must sit with them throughout (if the they leave the play area, they may not return). They cannot scout other teams' deck builds, but they can help with deck building as much as they wish.
During Team Matches
Fourth players must be with their teams from the start of the round. They must remain on the same side of the table as their teams and stay with them for the match. If they leave the table they may not return.
They can't consult notes or scout other matches during play or communicate with spectators, but they can communicate with their team as much as they wish, as long as doing so doesn't unduly hold up play. That means they can provide opinions on any plays, remind teammates about cards they might be up against, and point out triggers that might otherwise be missed.
While the fourth player cannot touch any cards, they can pretty effectively direct a match if they so choose. Luis Scott-Vargas had always envisaged playing Modern, for example, and intends to direct the Modern seat in Team Constructed given the opportunity, making a lot of the decisions but not touching the cards.
Not every team has a fourth player. Peru managed to make day two with a three-person team, which is still legal for team play. It should be pointed out that in terms of providing help and advice, any player when completed with their matches can join in with advice. As team matches are decided by two out of three players winning, this can mean that deciding matches are effectively four-on-four matches in terms of decision-making.
Stay tuned to see how different teams approach using their extra head to help with decision-making—just one of the unique elements of the World Magic Cup.