So to start the DLC you have to go to this cabin near Whiterun and there will be this guy named Elvar or whatever. He will ask you to go to the Chaos World. There is a portal activation thing on a random tree so you'll have to find it. Once in the Chaos World, you will talk to the leader Chaos dragon. This is where you will pick sides.
Advantages and Disadvantages for Dragon Slaying Side:
1. After you complete the questline, you will be able to craft new Dragon Soul armor. This can be crafted with dragon souls so it is hard work to get a full set. This armor changes to blue when a passive creature or person is near by, green when a friendly creature or person is near by, red when an enemy is near by, and black when a dragon is near by.
2. After you complete the questline, you will recieve The Blade of Corruption which has enchantments that majorly affect dragons.
3. After you complete the questline, you will also be able to pick a follower, there is five to choose from, Elvar, Gondelith,bla,bla,bla. These are all dragon slayers like you.
4. After you complete the questline, you can no longer enter the Chaos World.
Advantages and Disadvantages for Chaos Dragon Side:
1. After you complete the questline, you will be able to craft new Chaos Armor and Chaos Weapons. These can only be made in the Chaos Forge in the Chaos World. They are about as strong as Daedric, but they require different amounts of Chaos Souls and Pure Chaos. The souls can be found in the Soul Land, it is similar to the Soul Cairn in Dawnguard except it is red everywhere. The portal to this place is always open if you're on the Chaos side. It is somewhere in the Chaos World. To acquire the souls, you will need to chase down wandering souls and click a button to catch them. Pure Chaos can be bought from the merchant Chaos Dragon named IDK.
2. You will always have access to the Chaos World.
3. After you complete the questline, you will be granted a Chaos dragon follower which you can name as the leader chaos dragon creates the beast. It will still be friendly even if you hit it. It won't automatically attack things unless you or it is attacked or if you command it to attack. If it dies, simply go to the Soul Land and it will be right in front of you. Talk to it and ask it to follow you and once you leave the Soul Land, it will be with you. If you dismiss it, you can find it wandering around the Chaos World. Wait for it to land somewhere and talk to it and tell it to follow you again. You can rename it by talking to it.
4. After you complete the questline, wild Chaos Dragons will be friendly, unless you hit it more than 2 times in 10 seconds. If you got close enough, you could talk to the dragon and it will give you helpful tips.
5. #4 does not count for any other type of dragon.
6. Occasionally you will find Dragon Slayers hunting for Chaos Dragons or you.
Chaos World:
It is similar to the nether in minecraft but instead of netherrack it is dark stone. If you don't know what the nether is, it has islands and floating big rocks and lava oceans and a jaggedy tall ceiling.
You also get a shout on what ever side you pick. It is called Chaos Breaker. It's pretty much an outward Fus Ro Dah. When you shout, it turns everything around you into a ragdoll, like when they die, and then you blow all the stuff around you outwards with a big explosion. This shout uses up your half your Stamina, half your Magicka, and half your Health.
That's it CYA!