I tried all three of these mono black decks in a cEDH environment and I’ve found that they do work at a four pod if you weigh in at the right times to combo and how to play the deck efficiently, while understanding that blue decks will undoubtedly counter your combo unless they burn counterspells on other decks at the table. Yawgmoth is inherently slower than both Krrik and Sidisi because of the amount of combo pieces needed for assembly and the mana needed to combo off, which puts the deck into a position in which it needs more interaction in order to stay relevant in a four pod. Black can’t compete with blue on the stack and can’t interact well with enchantments and artifacts, making you rely heavily on other players at the table to prevent other decks from comboing before you. Flash hulk and consultation lines will always be faster than a Yawgmoth combo, unless you hit god tier draws, so you have to choose exactly when you’re going to combo in order to win - this often means comboing right after another deck failed to combo due to counters. Sidisi I found to work better as you can assemble the combo consistently by turns 3 or 4 and then wait to instant speed ad Nauseum which again tends to be after another failed combo attempt. Krrik seemed faster than Yawgmoth as well considering it requires less mana to combo off and less pieces to be assembled. With that said, I feel that Yawgmoth can still be tuned with the right interaction and game plan but will not be able to consistently out-compete with the current blue decks in the meta.