The Hivemind

Added in Battle for Azeroth Beta Build 25902, is a new multi-seat flying mount with unique abilities and effects:

Effect #1Apply Aura: Control Vehicle
Effect #2Apply Aura: Dummy

Server-side script

Effect #3Apply Aura: Mod Mounted Speed %

Value: 10%

Effect #4Apply Aura: Incerase Mounted Speed % - Stacks

Value: 10%

Note: This mount is not available in the game yet, although it's most likely that we'll see it be part of a secret hunt in patch 8.1

Based on the spell details, we speculate that the more players join the Hivemind, the faster its movement speed goes, increasing by 10% per person. The buff keeps stacking indefinitely, although is going to follow "normal vehicle rules" so there might be a limit to how many "seats" there are in the vehicle.

Here's a preview of how the mount is rumored to look like, datamined by Wowhead: