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Note: In the midst of writing this, Brian Green at Gamasutra posted his article "Rethinking the Trinity of MMO Design." To say I didn't read it or didn't take anything away from it would be ignorant and stupid. I read it and agreed with most everything he said. He goes into much more detail about the "trinity" itself, and it's worth a good read. My article, however, is entirely my own idea. Any similarities are purely coincidental.
"The Holy Trinity." It's a phrase that means different things to different people. To MMOG and RPG players, it refers to a common mechanic among RPGs which some may consider sacred. Others consider it an outdated artifact of years past. Whether you call it the holy trinity or tank and spank, it refers to the same thing; an unbreakable combination of a healer, damage dealer, and damage absorbing defender. While many games have made efforts to ditch the combination, it's often unsuccessful or ineffective. That won't stop people from trying, and it just may be with a little more effort and creativity.
The trinity is typically implemented with classes. Classes have become a staple in both MMOGs and RPGs. Typically different classes take different roles of the trinity in some way. Priests or Clerics are often classes that take on the role of healer. Warriors or Paladins take the role of tank. Mages or rogues are often in the role of damage dealers. One common deviation from this class system is a classless system. In classless systems, players are able to customize their characters with role based restrictions extremely limited or removed entirely. It is common for character made with such systems to become Jack-of-all-trades type characters. These "jacks" have average defense, average restorative capabilities, and average damage output. The result is a character that combines all three aspects of the trinity. To many, this is seen as an escape from the tank and spank tradition, but in reality, it is just another variation.
The key components to the functionality of the trinity are health and roles. The gain, loss, and restoration of health and the contribution of two or more role-specialized players makes up the core trinity mechanics. As long as there are elements that reduces the enemy's health, restores the ally's health, and damages the ally's health in a race to deplete the enemy's health first, there will be a strong grounding in a trinity based foundation. To avoid the trinity, you have to avoid this role-based health race. To avoid that, you need to start from the beginning and come up with new win-lose scenarios that don't involve both health and roles. In these scenarios, loss doesn't necessarily mean death.
What conflicts and conditions could be used to indicate victory and defeat? I'll give some examples; points, morale, positioning, and endurance.
Like in fencing, points for solid blows could be awarded, and the first person to reach a set number of points would be declared the victor. This mechanic might not be fitting for a live battle, but it could be a suitable method of dueling. It wouldn't, however, work in place of anything in many current games. Most currently available games use a targeting system that doesn't distinguish parts of the body or even utilize realistic ballistics for projectiles. This method would be more suited to a game whose combat controls are more complex and focus on precision.
Loss is decided when one player has been beaten into a conceptual corner or checkmate. Certain actionssuch as countering advantages, striking critical blows, or being outnumbered, trigger changes in the ebb and flow of morale on the battlefield. When a player's morale has waned, the next blow would be a mortal one. This back and forth experience is suitable for a theatrical or dramatic combat experience. Changes in players' morale could be more drastic when their morale is particularly low. A lucky critical hit while on the verge of defeat could even turn the tides. In a game with simplistic hit detection or sticky targeting, controls and camera could be automated, and special lighting and music could be put into effect. This sort engaging device could really draw the player in.
For particular events or encounters, win/loss could be decided by maneuvering a target into a location of vulnerability. The difficulty of which would be dependent on the scripting on the enemy. For example, you may defeat a giant bull by causing him to charge into a stone wall or off a cliff. For regular play, certain team-based abilities may be only accessible in a specific arrangement or formation. While the player is trying to enact the perfect sequence of moves to get the target to drop his guard and move into position, the enemy may have a totally different target position for party-defeat.
The first player to strike a certain number of times in a row wins. Each attack drains a slowly filling energy pool. If one player has enough energy to strike back, the battle continues. Pacing and defense play a pivotal role. Different situations or abilities could trigger an increased energy gain, granted an advantage.
Certainly these ideas are kinda far out, but that is the point. By eliminating what we're used to and comfortable with, you can come up with ideas that are truly unique. Out of that wacky, illogical, or even pointless uniqueness, you may find a mechanic that leads you to excellence. Classes are not necessary. They're certainly not necessary for role-based gameplay. Additionally, stereotypical role-based gameplay is not necessarily the only or best way to design every game.