Stormwind Skychaser is one of the BlizzCon 2017 special (virtual) items. It is available both to BlizzCon ticket holders and to those who purchase BlizzCon Virtual Tickets.
This is a flying mount and its flying speed depends on the riding skill of the character using it.
It includes a passenger seat, so it is able to carry two characters.
The /mountspecial is the skychaser visually moving back a couple feet and firing twice from its two cannons.
Stormwind Skychaser is one of the BlizzCon 2017 special (virtual) items. It is available both to BlizzCon ticket holders and to those who purchase BlizzCon Virtual Tickets.
The Horde counterpart is Orgrimmar Interceptor.
Official video from Blizzard: