Today, the Crimson Stallion mount is (was?) on sale from murlocs.
To buy the mount you need a secret ingredient which you cannot trade during common murloc trading game. It is obtained from Murloco cavern event in the middle of Nazjatar for 666 gold, and unlike other murloc items does not disappear the day after.
The event is simple: you need to camp the cavern until naga spawn there. Kill them two guardians, you will get few waves of three and a “boss” – all easily soloable. When you kill naga, Murloco is released from the cage, and you can use him as a vendor for 5 minutes, then he disappears.
The trick is that the event has an unknown respawn timer – and a very long one, several hours. I did as advised by Wowhead folks and hopped through realms until nagas spawned (on my 5th try). The much desired taco is mine! Btw, you can’t stock them – you can hold only one at the time.
When I returned to the murlocs, I started trading… only to find later that Crimson Stallion disappeared from the trade and got replaced by another item! It was not a reset thing, because I saw him first half an hour after reset.
Lurking more, I discovered one interesting thing: this mount availability might be phased. So, the phase in my case may have been triggered by joining multiple groups in search of Murloco. Imagine that :)
Rumors are, it depends on War Mode. I will try to turn it on in the evening and see the vendor table again. If not, it’s joining multiple groups again until it procs – because it’s definitely available until next morning.
Don’t be daft as myself – get your taco in advance, and check for the stallion availability in both war mode on and off daily :)