So yesterday I added in an earthquake event. It's a pretty simple thing, every once in a while there will be an earthquake that shakes things up and will damage things nearby. However because there are so many systems that work together it has a bigger impact than you'd expect.
Everything in the area getting damaged a little bit will probably be minor to the player, except when they are foolishly running around with low health. It will usually flatten fragile things like barrels and crates. Really unstable things are going to cause problems, like exploding barrels and energy vortexes will go boom. Of course this can set off a chain reaction of other unstable things.