When Universes Beyond was first announced, Wizards of the Coast said the mechanically unique cards would be restricted from the games Standard format, which generally allows cards from the most recent sets
Katerina of Myra's Marvels Katerina of Myra's Marvels falls into a similar category as its marvelous co-workers, but its effect is a little less specific and has a better payoff
One other interesting note with the summons, is they are Creatures, so they could be copied as such to get even more continued value
Just cast big Demons like Dread Cacodemon to chip away at whatever life your opponents have left
It is also BFFs with spellslinger strategies
Sai, Master Thopterist is the most flexible among legendary creatures with this play pattern, as there are plenty of strong artifact-centric strategies that synergize with its effects for building an army or drawing cards as the situation warrants