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
Bumbleflower Face Of Peace Offering The face commander of the deck, Ms
Glen Elandra Archmage 3.0 This is to control decks what Sower of Temptation is to beat down decks in that if it is not appropriately dealt with the game shortly concludes
In theory, so long as you Rule Zero it in with a proxy, Providence of Night is entirely playable on paper, too
Use Energy Burst to hit for huge damage, and then join the Ghost Dog Pokmon Greavard on an Underworld Stroll to mess with your opponent's hand