This guide will tell you how to tame a number of creatures from Battle for Azeroth zones that are normally friendly. The trick involves a toy: N'lyeth, Sliver of N'Zoth. This trick was first reported on our forum in Feb 2020, and was used by the Secret Finder Discord to discover how to tame some unique cloud serpents.
This trick is only for friendly creatures in Battle for Azeroth areas, so: Zandalar, Kul Tiras, Mechagon, Nazjatar, and the assault phases of Uldum and the Vale of Eternal Blossoms. The creatures may also be friendly to one faction but already-tameable by the other. It also requires the creatures to be flagged tameable, which most friendly creatures aren't. The few that are are normally not intentionally flagged, but none of the ones we mention here are disruptive to the game if tamed.
Unfortunately you can't at the moment. It appears that one of the quests required for obtaining N'lyeth, Sliver of N'Zoth has stopped working. Until it's fixed - assuming it gets fixed - this page will only be useful for hunters who already have the toy. Sorry!
For most creatures: just turn War Mode on, proceed to the creature, activate N'lyeth, Sliver of N'Zoth and tame away! Note that the toy has a one-hour cooldown, so it's safest not to use it until you need to. Its effects are also lost if you ever leave Battle for Azeroth areas, hearth, or take a portal, so plan accordingly.
The Ivory Cloud Serpent is a little more complicated. Like all cloud serpent tames, unless you're a Pandaren you must purchase and learn the tome "How to School Your Serpent", from San Redscale at The Arboretum in The Jade Forest. The resulting skill is account-wide and the tome can be purchased and learned by any character on your account, of any faction, that is Exalted with the Order of the Cloud Serpent. You must also have turned War Mode on.
The Ivory Cloud Serpent spawns once every ~2-3 hours in the Vale of Eternal Blossoms, but only on days when a Mogu assault is in progress. This only happens every second week, for a few days of that week. It won't appear at all on weeks when a Black Empire assault is happening. It's also best to pick a time of day when nobody else is camping it, or players that are trying to lasso it for the mount will get it before you can.
You'll need to wait for the Ivory Serpent to spawn just a little south-west of the camp and bonfire at Winterbough Glade - coordinates approximately 27,55. Don't use the N'lyeth toy yet! While you're waiting be mindful that PvP players may try to kill you. If you're too high in the air you'll receive slowing debuffs from the Great Worms From Beyond flying overhead, or they may run into you and kill you. If you're too low, PvP players will be able to attack you more easily. A rare-detecting add-on, such as Silver Dragon, can be of use in warning you that the serpent has spawned.
When the serpent spawns it will start flying rapidly to the south-west and perform a roughly clockwise circle of the Vale. You shouldn't try to follow it, but instead fly directly west, to the top of the Gate of the Setting Sun. Land on the ridge on top of the Gate, just a few tiles north of the southern end, and face south and wait for the Ivory Serpent to approach. If you were quick you should arrive with some time to spare. Drop a Freezing Trap along the ridge, closer to the south. For good measure drop a Tar Trap even closer to the edge to give you more time to react. As soon as the Serpent nears the Gate, and before it reaches the traps, activate your N'lyeth toy making you hostile to it. As soon as it hits the Freezing Trap, tame away and hope that nobody arrives and tries to attack you. Good luck!