Without Dyfed, Yawgmoth might never have risen to become The Father of Machines
It breaks even in terms of how much total additional power and toughness you get with a traditional Anthem at three creatures, but giving one of them +2/+2 instead of +1/+1 can really change the texture of combat, and things get out of control once you have four or more creatures
Sauron, Lord of the Rings
Look for cards that can repeatedly untap themselves and/or sacrifice things for free like Blasting Station and Ashnod's Altar to establish combos, since free or close to free is important for many loops
Using the Undying mechanic, Yawgmoth can quickly get into infinite combo situations where he continuously draws cards by sacrificing Undying creatures
Most commonly, youll play them during your opponent's turn at the end step, during combat, or in response to other spells and abilities