There are so many ways to try to combo off with Bolas's Citadel, whether thats various kinds of storm decks in Modern, Jund Citadel in Pioneer, or that deck youve seen in Historic with Bartered Cow and Refurbish
Without the Cauldron combo, it can be difficult to win against the more streamlined decks in Pioneer
From Mark Chalices The Machine (Hells Caretaker) deck, to Stephen Menendians Alan Comer-inspired 1995 era Reanimator deck, to modern adaptations of Vintage Dredge, Bazaar is the glue that holds together Reanimator decks across eras, enabling necromancers to quickly and consistently dump creatures in the graveyard, while tearing through their deck to find reanimation spells
Emrakul makes short work of most people and is pretty hard to stop
The defender matches up their blockers with the attackers they want to block