The Godsworn Champions of Ruin can be seen as the default battalion for the Age of Sigmar Slaves to Darkness army. The basics of this battalion is that you have a general and 3 to 8 Slaves to Darkness units. Using this battalion organisation you can create well rounded army lists that are both flexible and decimating.
The organisation options for the Godsworn Champions are quite open. You need a general. The General could be a Daemon Prince, Lord of Chaos, or a Sorcerer Lord. The last two could be mounted on a manticore. My suggestion would be to o with the Daemon Prince, or as a second choice the Lord of Chaos. This is because you can take a Sorcerer Lord in the main body of the battalion.
For the main body of the battalion you can take one to eight units that can be selected from the slaves of darkness list. Most of the slave to darkness units are listed with notable exception of the Chaos Marauders in any form (on foot, horse or chariot).
The openness in the battalion organization gives you a great deal of flexibility. Of course there are some units that you will want to add in all the time, like at least one unit of Chaos Warriors and a Sorcerer Lord, however this still gives you plenty of slots to add in other units to make in your army. I do highly recommend adding a unit of Chaos Knights. This will add speed to your army.
Battalion Abilities – Unholy Challenge
The benefit of this battalion is that you can pick a unit from the battalion that is within 3″ of a Hero or Monster, for example in combat, and that unit can have a free assault round. Now the warscroll is written with the expectation that you will assault the Hero or Monster that you are near, but the rules are not explicit on this.