This is one of the hardest achievements in the game though it is so much easier once you figure out how to do this and get on lady luck's good side to start.
Once you load the game up, enter wraith mode and open up your map. If you see a green intel icon go there immediately and get the intel. If you do not see anything quit and restart. Sometimes you will get multiple intels on your map. What you want to do is try and get Ukugagu. He is probably the best guy to get because he is a tank. He is good at staying alive and isnt too OP. Zugor is quite OP and can cause issues by killing the captains or body guards before you can eat them with a graug. Once you get one of those two battle them and defeat them so they drop to their knees and you get the option to dominate.
I ended up with Zugor so I tried to make the best out of the hand I was dealt. What I did was grab a graug after getting Zugor to appear and tried to eat as many of his 4 captains as possible. I got two of them and he killed the graug. So I beat him, trick to beating him is to build up your combo and shoot the fire arrow at him. Using the wraith punch + slashing will accomplish this.
Once you dominate him, you will want to command him to attack other warchiefs. Go for the ones with body guards. Below you will see a link and it will have the graug bait locations,
https://steamcommunity.com/sharedfiles/filedetails/?id=51799...Use the Graug bait when you start the riot and eat the body guards then the warchief. After the battle is done, grab your warchief and command him again to another warchief. Once you send him away consume the Uruk under your control(You want to do this after commanding because it will kill your warchief if you dont send him away. You will get a lot of points plus 100 ponts for Graug kill.
Rinse and repeat until no warchiefs are left. I would then focus on the remaining monster kills needed by rioting the captains and once you hit your 10 kills start advancing days to get new Warchiefs and Captains. You do not need to worry about Captain kills, when a Captain is promoted, it counts it as a Captain's death but also removes a warchief death because there is now 1 more warchief now. The benefit of making new warchiefs is that they will get bodyguards making it quicker to get the other captains so you could actually probably just promote them and still get your monster kills.
TIPS:
-Remember to kill your followers after commanding the warchief to get points for all the kills plus Graug
-Mount Caragor's and Graugs whenever you see them during your playthrough. Killing them nets you 100 points per kill. Easy points with Caragors. They are everywhere.
- As mentioned above Killing a warchief nets you good points so you will want to advance days to get captains promoted. Plus those warchiefs make bodyguards out of the remaining Captains, which allows you to kill more in less time. So try to let a bodyguard escape once and a while.
-Avoid travelling. You have the ability to fast travel. Abuse it!
-Always fast travel to the next Riot area EVEN if it is at the same location. This is the only way to get the Graug bait to respawn.
Always check the surrounding area for a Captain after your riot. You might luck out and find one nearby. I had on occasion some interrupt my riots as well.
I actually finished at 30 mins but still needed points so I spent 9 mins killing graugs and Caragor near my warchief so I could kill him once time got close.