Ikoria

Ikoria is a plane from Magic: The Gathering that we really don't know too much about since it's coming in a later set. We only really know three things about it:

1. Vivien Reid is there and she's living her best life.

2. There is a keyword called Mutate in the set that allows you to create your own creatures, which was teased in Un-sanctioned.

3. This set may introduce the first official appearance of "keyword counters", which work like +1/+1 counters but grant keywords instead. It is unknown whether or not this ties into Mutate.

We also know that Ikoria is a "bottom-down" set, meaning that the mechanics come first, and flavor comes later. That usually means there isn't much in terms of worldbuilding but that will have to be proven.