A lot of games are made up of interlocking systems.  I think it might be useful to pull these systems apart and see what makes them tick.

A classic example of what I mean is the X-COM series of games.  X-COM games all feature an overarching game system where you construct bases, buy weapons, hire staff and research new technologies.  (In the first 2 games this was called the “Geoscape”.)  Occasionally an opportunity for combat will arise in the game, and you will send forth your agents to meet the foe.  (The first 3 games used a turn-based tactical battle system; Interceptor had space dogfights, and Enforcer was more of an FPS with RPG-ish skill progression.)

The cool thing about the X-COM games is how the two systems interconnected.  Your agents were situated at the bases you constructed, and that influenced how quickly they could intercept the aliens.  They were equipped with whatever you bought/researched/manufactured.  Afterwards, any items scavenged from the battlefield (assuming your soldiers weren’t completely wiped out) could be used as you see fit.  The alien items would often open up new lines of research, allowing your soldiers to equip themselves with alien weapons, or even allowing you to construct new hybrid human/alien technology.  If nothing else, you could sell the spoils for cash.

For an example in a very different sort of game (OR IS IT?), let’s go for Pokémon.  Most of the Pokémon games are similar to what people call “role-playing games”, but they have their own flow that revolves around collecting the titular monsters.

• Start with one monster.
• Battle wild monsters to catch them.
• Battle wild monsters to cause your monsters to build in strength.
• Battle NPCs to allow you to advance the plot and get to new areas.
• New areas have new monsters.

It’s a straightforward cycle of increasing in strength.  Monsters have different abilities, so reaching a new area will let you do things you could never do before (by catching monsters with new abilities).

But you’ll notice that I haven’t discussed the battle system at all.  Pokémon’s battle system is not too difficult in theory: Each monster has various abilities that have different attack strength calculations.  Monsters and abilities have elemental affinities that fit into a huge graph of relationships (imagine rock-paper-scissors to the 5th power).  You can have six monsters “ready” at one time and switch between them during battle.  There are also abilities with strange effects, like “self-destruct to knock myself out but cause huge amounts of damage to the opponent”.  And so on, and so forth.

There are several links between the systems.  The “plot” advancement doles out new abilities and elemental affinities in a steady stream.  Wandering around, you can search for the best places to train your monsters.  Training itself can be complicated as you pick and choose which abilities to let your monster learn.  There are also helpful items you can accumulate.  And of course the battle system acts as the resolution mechanic for the overall game.

So what?

What we’re really doing here is studying the ways different game systems can interconnect.  This can help us understand why games are the way they are, how they might be improved and what other possibilites exist.  For example, an RPG-ish advancement “frame” coupled with a match-3 resolution mechanic is the recipe for Puzzle Quest.  The later X-COM games attempted to replaced the tactical battle system with other resolution systems (with, sadly, unpopular results).  And so on…