Fimbulwinter

Fimbulwinter or Fimbulvetr (mighty winter in Old Norse) is a prophesied event affecting several realms such as Midgard, @Svartalfheim, @Vanaheim, @Alfheim, and possibly others.

It is a three-year long period of extreme environmental change (e.g., heavy snow and blizzards in Midgard, increased humidity in Svartalfheim and Vanaheim) which serves as a foreboding occurrence for Ragnarök, the total annihilation of all the Nine Realms.

Because of it being magical in nature, Fimbulwinter over time causes curses, magical items/weapons, and other blessings to weaken across the Nine Realms, some more than others, or disappear entirely. As a result, this was seen as either a boon or inconvenience

Beside Midgard's heavy snow and blizzards, the Fimbulwinter also affected most other realms. Svartalfheim has random and intense earthquakes as well as humid aroma, Vanaheim has extreme humidity in the jungle, Alfheim has violent flashes of Light in the @Lake of Souls, and @Helheim has also colder and darker places overrun with @Hel-Walkers. @Niflheim appears to be a frozen land again and no longer just a realm of toxic mist. However, @Asgard, @Jötunheim, and @Muspelheim suffer little to no effect from Fimbulwinter. It is hypothesized by @Mimir that the more primordial the realm is, the less it is affected.