Upon entering the battlefield, The Mimeoplasm can exile any two creatures from any graveyards
To exploit those strategies, you need to fill your graveyard, and Golgari Grave-Troll is one of the best ways to do so
You definitely get a lot of chaos with a cascade deck, but youre also building around a very powerful mechanic
In general, you Past in Flames is at its best against counterspells because of Flashback, and good for longer games where Ad Nauseam and Empty the Warrens are no longer good enough, but your graveyard is stocked with good spells to flashback
It may be a ubiquitous card, but it might also just be a card with a fair amount of utility
W/U fliers, W/U control, W/U aggro, W/U theme decks, mixing and matching for some classic stuff like Bant control or Jeskai aggro