To war, you need the captain to post the challenge in the Team Wars section. The other captain of the team being challenged needs to confirm. Within that same topic, the captains need to agree on a format to use.
Here are the formats:
Both teams pair off their players with a player of the opposing team (sometimes it's done randomly and sometimes it is not) and the players just duel their selected opponents. If the teams cannot arrange random pairing between each other, they may request a Judge to do it for them. The team that accumulates the most wins is declared the winner of the war.
The number of players on the line ups is usually an odd number in order to avoid a tie. However an even numbered line-up can also be used and in the event of a tie both teams select a player from their main line up to duel in a tie-breaker match.
A modified version of Brackets Format. In this version teams don't duel for points. Losers will be eliminated from the war, and the winners will precede and duel their next opponent. New opponents will be randomly selected the same way as before. This continues until a team is out of members.
This format requires opposing teams to create their line ups in a specific order with a certain amount of substitutes in case a player in the main line up is unable to compete.
The first match will begin with the two players elected to go first in their team's line up. The winner of that match will go on to face the number two player in the opposing team line up. This continues until one team is out of players. The team with remaining players at the end is declared the winner.
A modified version of Elimination format. Here you don't duel only from the start of the line up but also from the end. So it starts with the two players elected to go first in their team's line up and the two players elected to go last in their team's line up. Thus the name reflected. This is for those who like strategic style of Elimination format but want it a bit faster. This doubles its speed and creates new strategies among the teams. If a team has only one player remaining while other team has more, both first and last player can duel that remaining one.
This format requires opposing teams to create their line ups (no specific order needed) with a certain amount of substitutes in case a player in the main line up is unable to compete. Players can challenge any player from opposing team's line up. Playesr that lose one match are eliminated. The team with remaining players at the end is declared the winner.
This is an altered Crossfire format where you got to lose two matches in order to get eliminated from the war (all other rules from Crossfire format apply here as well). As people would like to say, you got 2 lives. If you lose a match (1 life), you can change your deck for the remaining life you got. Subs must have the same number of lives as the players they are substituting. However, if a sub has more lives than the player they want to substitute, they replace him by using lives he had (ex: you got 2 lives and player that goes out has only 1, so you are subbed in his place with also only 1 life). The team with any remaining players at the end is declared the winner.
This format requires opposing teams to create their line ups (no specific order needed) without substitutes. Players can challenge any player from opposing team's line up. Each team gets the same amount of hearts (agreed by the leaders). The number of hearts must be greater than or equal to the number of players. When a player loses a match, their team loses a heart. The team with any remaining hearts at the end is declared the winner.
A modified version of Hearts format. In this version for each 3 match wins a team makes, it also gains 1 heart. With this rule, team that is losing can come back easier when gaining hearts but also it makes the winning team gain even more advantage.
This format requires opposing teams to create their line ups (no specific order needed) without substitutes. Players can challenge any player from opposing team's line up. Teams play certain amount of matches set at the start of war (agreed by the leaders). The number of matches must be odd to avoid draw, starting from 7 which is the minimum. The team that accumulates more wins at the end is declared the winner. If there is a situation where one team is leading and opposing one cannot catch up until the end (lets say 7 matches are played and one team has 4 wins), the war ends immediately and leading team is declared the winner.
NOTE: Deathmatch format is the fastest war format where dueling is intense from the start. Unlike Hearts, here you cannot afford losing and coming back later, because you may not have the chance for it.
Rules During a War
Rosters cannot be changed unless both parties agree.
After each match, players must post the results (take screenshots just to be safe).
If a player has to leave during a match, the match may continue at a later date. Until then, neither player can participate in any other match until the said match is completed.
If new cards are released or if game rules are changed, the war continues using the same cardpool or rules that it started with.
If the official Konami Banlist is changed, the war continues with the same Banlist that is started with, where any necessary proxies should be determined.
Deadlines can be extended if both parties agree.
If a ruling dispute arises, look up the ruling and show your opponent what you find.
If a gameplay dispute arises, try to stay calm and explain the situation to your opponent.
If a player disconnects at any point in a duel, a game loss is issued, unless the said player has clear-cut evidence that he/she had an advantage in the duel (field/hand), in which case, a game win is awarded. In the case that there was no screenshot taken of the disconnecting player from either side, its as if the duel never happened and a re-do would be in order.
If a player disconnects during siding, a re-do would be in order. When this occurs, the losing player of the previous duel must immediately admit defeat, and both players will go straight into siding for the next duel.