The Citadel thrives in sacrifice and storm strategies, especially when paired with lifegain or top deck manipulation
This can make it have some less efficient cards and plays, but they do work together, as you will want to be putting cards into the graveyard to put them into play again
Flying.Whenever Hakka, Whispering Raven deals combat damage to a player, return it to its owners hand, then scry 2
Many blue cards are on this list, but card draws not strictly tied to that color, so every color makes an appearance
Yes, only drawing two cards from this isnt the biggest hand refill, but the ability to give a large creature trample without going down in cards helps you keep up with the rest of the table