The Power stat must be increased to the indicated value for Talion to unlock and upgrade new abilities.
Collect the indicated amount of Mirian to upgrade the corresponding attribute.
Kill a Morgul Bat, which appear near caves in Mordor. Enter the "Nature" section of the Appendices to read the following description: "Those Uruks that get poisoned become horribly diseased and bloated, wearing their deformities as marks of honor. The poison slowly eats at their minds, sending them nightmares of a demonic man-bat who preys on fear."
You can use Caragors as a mount after getting the "Ride Caragors" ability. To start, stand on a ledge directly above a Caragor and press R1   PlayStation3  or RB  Xbox One   Xbox 360  to jump over it. A quick time event will start, where you must move the pointer into the circle and press the indicated button. After successfully completing that sequence, Talion will be able to ride that Caragor. You can subsequently dismount it and it will remain loyal. During a battle, you can use the following commands while mounted.
You can also use captive Caragors as a tactic. When found in cages in enemy encampments, shoot the lock off their cells to have them distract and thin out the orcs. This is especially useful when capturing strongholds.
Note: This will take some time to prepare. Collect all 43 different Epic Runes and have the Dispatch ability. You must have at least 20 Captains alive; which is done easiest in Endless Challenge and Test of Wisdom. Select a Warchief that you will brand later. Send death threats to all the Captains and Warchiefs. Brand the Warchief that you selected earlier. Brand the 20 or more living Captains. Command all the Captains to become bodyguards of the Warchief that you branded. Summon the branded Warchief. Delete the Epic Rune to be duplicated, or it convert to Mirian. You should now have 42 Epic Runes. Kill all the followers. Upon death, every Captain and the Warchief will drop the same Epic Rune that you are currently missing.
Do not allow any of the Warchiefs to be killed before the final mission in the Bright Lord DLC. If that happens, the final mission cannot be completed because no new warchiefs will be available to be dominated. If you dominate all warchiefs successfully, the storyline will continue after the betrayal.
Go to a Forge tower, or ruins near campfires that have four floors (easier). If at a Forge tower, use Attract to bring enemies closer first. Stealth kill an enemy, and immediately climb back up and wait using stealth to check when you can stealth kill again. The enemies usually lose focus after short time, as long as there are not any archers that can spot you. "Height of Despair" will be earned after ten such kills.
Use the following steps to complete each of the challenges easily.