Achievement mounts will reward to character for completing some achievements. Once the Achievement complete, the mounts will be send to the character.

Once "befriended", a gronnling will happily carry its rider to their death.

Riding Requirements:

Level 40
Journeyman (150) Riding
Source:

Achievement: Glory of the Draenor Raider
Notes:

This mount is the reward completing the first tier of Draenor raid achievements.
Travel Mode:

Ground (+60% or +100% speed)
Speed depends on your riding skill.

Gorestrider Gronnling: