Adding white gives you access to absolute zombie bangers Corpse Knight and Wayward Servant, and the card filterings perfect for burying a ton of zombies in the graveyard for a mass reanimation effect
From the cards already revealed it seems that Tera Pokemon will be the primary focus of this expansion, with cards like Briar granting massive benefits to those already powerful Pokemon, and several powerful new Tera Pokemon ex joining the fray
[c]Niv-Mizzet, Parun[/c] is a very popular commander because he has an infinite combo with [c]Curiosity[/c]
I could go on about why these creatures are good in affinity but with the majority having been constructed staples in the deck I am sure there is more than enough literature out there already on why they are good
If they have copious amounts of graveyard hate, you can move away from Witchs Oven and Cauldron Familiar as well
Achieving inevitability is always the first step and the top priority when building a control deck