My general rule of thumb is that for every two MDFC lands in my deck , I cut one land
Most importantly, you can find cards that seem to have been heaven-sent for your strange little deck that are so oddly specific to your commander they cost literal pennies to pick up
Inventive mono-black players are also including Spiteful Hexmage and Hopeless Nightmare as ways to get easy draws off Braids, Arisen Nightmare, and using Beseech the Mirror to option their way into Sheoldred, planeswalkers, sideboard cards or a sneaky Rankles Prank
It exiles all permanents from the game and makes you discard your hand
Their iridescence is really great to look at (granted, for early EX, like @wisewailmer said, they really have to be pretty much mint to look really good)
Go south to find a set of 3 Pok Balls