This mod adds a mechanic to ride Durnehviir. This mod adds the "Call Durnehviir" ability to the player upon completing stage 60 of the Durnehviir quest (DLC1VQDragon), in which Durnehviir teaches you the last word of the Soul Tear shout. If you have completed that quest stage already, then the ability will be added to the player on start up after installing this mod.

The "Call Durnehviir" ability is added to your powers in spells. It equips like a shout and is activated the same way. It is an area of effect so you do not need to target Durnehviir when activating. Once activated, Durnehviir will land next to you and you may mount him by approaching and activating him.

How this mod works:
I created the spell, Call Durnehviir, by copying the Tame Dragon effect from the Dragonborn DLC Bend Will shout and made it applicable only  to DLC1UndeadDragon race.
I modified the DLC1UndeadDragon race to allow mounted combat. (I checked the box in the dialogue tab for that race.)
I modified the Durnehviir quest to add the Call Durnehviir spell to the player in the last stage of that quest.
I added a quest which checks to see if the player has completed the requisite stage of the Durnehviir quest and, if so, automatically adds the Call Durnehviir spell to the player.

Compatibility
This mod will not be compatible with other mods that reset the "Allow mounted combat" check box in the DLC1UndeadDragon race tab or change the Summoned Durnehviir's race.
Any mods that replace the quest fragment script for quest DLC1VQDragon are not compatible unless you have already completed stage 60 of that quest.
This mod is compatible with Durnehviir God of Death which I recommend.

This is my first mod. I would appreciate feedback and help on making it better.

Please do not upload this mod anywhere else. If you would like to incorporate any of this mod into another mod, feel free, but please give me a shout out if you publish it.