* the emergent gameplay: as defined in WikiPedia, "complex situations in
video games, board games, or table top role-playing games that emerge from the interaction of relatively simple game mechanics". The (custom) engine we are using is designed using a pattern called "entity, component, systems", which - without going into details cause I'm not sure how interesting it is except for programmers ^^' - allows us to do just that: create a basic set of rules for how all entities in the game interact. I'm talking things like "fire burns", "electricity travels down to the closest entity within a certain range" (I didn't say the rules were scientifically accurate ), "blood puddles slow you down", etc. What the player makes of these rules, and how he chooses to exploit them is what creates the complex and often unforeseen situations.
Sometimes the results are funny / borderline-bugs: one rule says "fire propagates to entities within a certain range". Normally a fire has a "lifetime", after which it dies out, but if you set fire to two entities close enough, then re-kindle the fire of one of the two entities at the right time, you can create a self feeding cycle of fire where each entity sets fire to the other one before burning out :D
Other times the results are really cool: originally we had the laser gun create a short-lived flame, just a few frames, on the targets it hit - cause, you know, lasers are hot? Well once while playtesting, I hit an enemy with a laser at the exact moment he was shooting at me: the laser created a small flame on the point of impact on the enemy, the small flame ignited the bullet, the flaming bullet came hurling down at me, lodged itself into my leg, and set me on fire...
This sequence of events was not something I scripted or had even anticipated would ever happen - remember, this is just a rule that says "fire burns", nothing in the code specifically handles setting bullets on fire in such or such case. So this somewhat complex situation unfolded thanks to the interaction of several systems that define the rules of the world: and this is exactly the sort of gameplay we are trying to create, a sort of TCE-AB sandbox where we give players the tools to have fun in their own way, and discover their own ways to beat or break the rules of the game!