They are mainly useful for deterministic combo loops where the same prompts, priority passes, targets, mana choices, and stack-order decisions repeat several times
The plane of Dominaria was the birthplace of the shadow mechanic, so maybe well see shadow again on a return visit, but its a fairly small possibility because R&D avoids putting parasitic mechanics (i.e., mechanics that only work with themselves) in modern sets
I think almost every Steel deck moving forward will run this Kida card as a sure way to protect their characters before they can start playing their more powerful ones
And it can also do a lot of manga in the late game when you need it to
It never saw the light of day in Modern or Extended
Here is how the combo works: activate Duskmantle's ability, and tap Ghoulcaller's bell so each player mills 1 card