When playing on the Eternal realm, there’s both a Helltide whisper requiring players to seal Chaos Rifts and, since today, the Piles of Phials buff increasing Horadric Phials drops, both of which are (or were) exclusively mechanics of the Seasonal realm if I’m not completely mistaken
If I am mistaken though, Chaos Rifts don’t seem to spawn and Horadric Phials don’t seem to drop on the Eternal realm…