For those who do not know, Crusader Kings 2 is a video game about being noble dyansty in the middle ages, with all the intriege and (often literal) backstabbing that entails. One of it's features that was added in a DLC is the Chroniclers, which write down the epic deeds of your ruler and house, such as when you go to war, join a Crusade, or aquire a higher noble rank. However, in the quiet years of the Kingdom, between the Viking raids and the Dues Vults against the infidels, your Chronicler will add... interesting events. These include good harvests and Earthquakes to the sitings of giants, sea serpants, multiple suns, and dragons.
Crusader Kings 2 isn't a 100% realistic game. There was a massively ahistorical DLC pack that added an Aztec invasion that could happen over five hundred years before the Aztecs were even a thing. However, the developers at least have given historical accuracy the old college try when it doesn't conflict with the gameplay.
So, did the Medieval chroniclers clearly add events to spice things up in the dull years or outright supernatural events to their long tales?
Yes and no.
Yes, because medieval chroniclers regularly included accounts of portents, miracles, astronomical events, sightings of dragons and other events we would today call supernatural, as well as non-political events such as famines, cultural trends or unusual weather.
No, because they didn't write these things just because they were bored, or because nothing interesting happened that year in a ruler's life. Much like the news nowadays, medieval chroniclers weren't just concerned with the doings of one family, however important, but focused on everything that the author considered significant or important. Famines, extreme weather and notable cultural trends all make the news today, and they were similarly featured in chronicles. Local chronicles tended to feature more obscure or small-scale events, in contrast to so-called universal chronicles, which were often written at or near royal courts, and had much wider interests - think local and cable news today. So it wasn't that chroniclers just 'filled in' gaps with made-up or irrelevant stuff: they were conscientious editors, carefully selecting and framing the stories and events they included in their work. They were human beings, and different chroniclers had different interests and styles with are quickly apparent. Some, like Lampert of Hertsfeld, an 11th century German chronicler, were intensely political and detailed, while others were laconic and not afraid to leave entire years blank. The notoriously terse Irish Annals of Ulster' have a famous entry, where the entire year was summed up in a single sentence:
There was a great wind this year.
The other issue to address is 'supernatural' events, like miracles, dragon sightings etc. These were routinely included in chronicles, again, not as made-up events to spice up dull years, but as real events, which were believed to have occurred and were significant. While no historian believes that there were actually flying dragons and talking dogs to be found in medieval Europe on a regular basis, medieval people did. They weren't gullible fools either - there is a huge amount of ink spilled in the middle ages debating how to distinguish real miracles from the frequent scams and cons. But, for medieval chroniclers, these events were real, and were just as, if not more important, than the conquests or deaths of kings and emperors.