Ur'zul Fleshripper

Coming in Patch 11.0.7.

This terrifying Ur'zul incorporates its latest victims into itself, creating a nearly unstoppable monster. Good thing you are treating it well, or you might be its next treat.

Riding Requirements:

Level 10
Apprentice Riding (ground)
Expert Riding (flying)

Source:

Aridormi in Krasus' Landing, Dalaran (Broken Isles).
Cost: 5000
Only available during Timewalking

Notes:

Added in Patch 11.0.7 as part of a Timewalking rewards update, this horrifying red Ur'zul can only be purchased during Legion Timewalking events. Purchase requires Timewarped Badges, which are earned by running Timewalking Dungeons during the events, with a bonus 500 by handing in a quest item which drops at the end of your first dungeon for the event.

Travel Mode:

Ground (+60% or +100% speed)
Flying (+150%, +280% or +310% speed)

Speed depends on your riding skill.

Other Mounts Using the Same Model:

Shackled Ur'zul

Green Ur'zul

Grey Ur'zul

More info on Wowhead:

Ur'zul Fleshripper taught by Ur'zul Fleshripper Bridle