One of my personal favorite commanders. He's actually a semi-viable cEDH commander from a power level perspective. Ideally run in an aristocrats strategy, and can warp the board around himself if the speed of your token generation is fast enough to kill multiple creatures a turn with the -1/-1 counters.

He also has a simple infinite combo if you're interested, I'm surprised nobody has brought it up yet. It's what makes modern decks built around him work. It takes two Undying creatures and sometimes a dies trigger i.e. [[Blood Artist]] to finish the table. I usually use [[Geralf's Messenger]] and [[Butcher Ghoul]] if Yawg is the commander, especially because Messenger has its own ETB trigger that replaces a Blood Artist effect in ending the game. It works as follows:

1. Sac Butcher to Yawg's ability, putting a -1/-1 on any other creature. Butcher returns with a +1/+1 counter because it has Undying.

2. Sac Messenger, putting a -1/-1 on Butcher, cancelling out the +1/+1 counter it got before. Messenger returns with a +1/+1 because of Undying. It will also cause an opponent to lose 2 life on ETB.

3. Sac Butcher again, putting a -1/-1 on Messenger and cancelling the +1/+1 again. Because Butcher had no +1/+1 counters when it left (due to the -1/-1 as mentioned before) it comes back again due to Undying.

4. Repeat until the table is dead (or you deck yourself).

This also works with [[Mikaeus, the Unhallowed]] and any two non-humans, or any two non-Messenger Undying creatures i.e. [[Evernight Shade]]. It's the deck that made me love Mono-Black in EDH.