Emergency codes are a Phantasy Star Online 2 (PSO2) game mechanics that revolves around introducing random dangerous events in the middle of an ordinary level. They range from cute rescue/capture missions to brutal simultaneous boss fights, which has a way of spicing up your random run quite intensely. Now PSO2 is a Japan only release (although it has been promised initially for US and EU but well), so it's likely you've never heard or seen it. Thus to illustrate this suggestion, here's a couple random youtube vids that hopefully will help understand how this works and how it could fit in this game, especially after announcements years back of the arcade redux which told something about "unpredictable events".
https://www.youtube.com/watch?v=qdOOnamBEVU
https://www.youtube.com/watch?v=vOevHLRk0Jo
There's a lot of codes but Clone and Duel are some of the more intense ones, they're a huge gameplay boost.
Hippo out
This is actually a pretty common feature in MMOs nowadays. You see it in Guild Wars 2, Rift, that Defiance game adaptation, and many more.
It wouldn't be hard to introduce into this game, we already have scenario rooms afterall.