Meta Teams

The metagame is "any strategy, action or method used in a game which transcends a prescribed ruleset, uses external factors to affect the game, or goes beyond the supposed limits or environment set by the game" (1). In the case of Mann vs Machine, the metagame consists of a predeveloped set of rules, classes, weapons and upgrades setup. One of the main purposes of the meta is to endorse a method which works most of the time, while at the same time attempt to familiarize and introduce core concepts and game mechanics about the gamemode itself. However, a limited setup wields its disadvantages, too, and as such, players must be encouraged to drift outside of the meta's delimitation if it is ever required to consider cases outside of the common spectrum. Some waves and missions posess ideal setups than can guarantee survival, but in further missions, each and any class and setup can get its peak performance because of a mission's composition and, in most of the cases, player skill and efficiency.

A meta setup isn't necessarily the most optimal setup for a mission. Due to the vast amount of combinations and perks from every class in Team Fortress 2, there is no such thing as a "perfect" team, but some setups can work considerably better than others with skill, effort and knowledge. While the meta can teach some core knowledge, "breaking the meta" unlocks a wide spectrum of skills and strategies that result in an optimal and smooth gameplay.

Meta teams (AKA "needed" formation) is a common sight around MvM servers. After the "Two cities" update, many people started developing a strategy to "easily win" missions. The standard meta consist of Soldier, Heavy, Demoman, Scout, Engineer and Medic.

When entering an MvM server (especially Mann Up), unexperienced players are quick to demand any of the classes listed above. If someone dares to change classes or being a duplicate, the kick threat is layed upon. There's even sights of MvM veterans that despite completing the missions 100+ times, still graps to this group of classes even if another veteran is confronted.

Sources:

(1) Metagaming. (n.d.). Retrieved February 13, 2015, from http://en.wikipedia.org/wiki/Metagaming