Patch 12.1: Curse of Ula'tek
new mounts listed by source
Patch 12.1: Curse of Ula'tek introduces us to the venomous
Dungeon Mythic Keystone Rewards
Mythic Keystone rewards now have a third tier of eliteness, with an 'Umbral Champion' mount for the top 1% of players in your region.
Miscellaneous Scenario and Instance Achievements
A sinister red serpent golem is available for those who dare the Season 2 delve boss in his lair at the highest level of difficulty.
Miscellaneous Zone Activities
Mounts can be earned from various activities on the coilded isle, including finding treasures, and completing acitivities in the 'Vaults of Atal'Utek' sub-zone.
Raid Meta-Achievements
This crimson feathered serpent is the meta-achievement reward for The Venomous Abyss raid added in Patch 12.1.
Prey
Two green mana wyrms can be earned through the Prey system in Season 2. One can be purchased in Silvermoon, the other has a chance to drop from a new Prey boss that must be unlocked via a quest chain.
Dungeon Boss Drops
There's a chance of looting this pale writhing serpent mount from Zul'jan in the new Altar of Fangs dungeon. There's currently no mention of it being restricted to any difficulty level.
Raid Boss Drops
This purple feathered chimaera drops from Ula'tek in The Venomous Abyss raid on Mythic difficulty only. As with previous mythic raid mounts, it's likely to be a guaranteed drop while the raid is current and after that it should continue to drop at a rate of 3 per kill until Midnight ends. After the expansion has ended it will probably have a very low (~1%) drop rate.
Reward Chests & Loot Boxes
There's a chance of looting this green-gemmed arcane golem from a Sturdy Chest loot object which can be found in the new Gnarled Isle delve.
World Boss or Rare Drops
These two colourful, serpent-themed mounts can drop from new rare NPCs around the Coiled Isle.
Battle.net Shop
These mounts are all listed as coming to the Battle.net Shop but at the time of writing we can't give any dates, or even confirm that they'll appear during this patch. The broomsticks have a Hallow's End pumpkin theme, so it seems likely they'll be offered by late October and the sheer number of them suggests that they may be offered as a bundle. But this is purely speculation at this stage!
Arena
Continuing with Midnight Arena's goredrake theme, the Season 2 reward is a toxic green.
Vicious Mounts - Rated PvP
Two armoured thornmaws (at least that's what seems to be under all that armour!) are the theme for rated PvP Season 2.
Mount Quest Chains
This spectral eagle is the reward for completing a quest chain in the Vaults of Atal'Utek on the Coiled Isle.
Non-Player Factions
This patch introduces two new factions that offer rewards: 'Captain Tokka' is a tortollan NPC and faction devoted to Cursed Fishing on the Coiled Isle, while 'Zul'jarra's Forces' renown is earned through various activities around the zone.
Standard Purchases
The Corrosive Coins required to purchase the Caustic Venomfang are dropped by various NPCs in the Vaults of Atal'Utek sub-zone. You can obtain the Corroded Soul Crusher for a token amount of Voidlight Marl after progressing your Delver's Journey to rank 5 in Midnight Season 2.
Trading Post
These mounts have been linked to the Trading Post but it doesn't mean they'll all appear in the near future - maybe not even during this patch! The next month's Trading Post inventory isn't commonly announced until close to the end of the previous month. We're listing them here because they first appeared in the game database in this patch.
New mount looks that have not yet been implemented
These mounts have actually appeared in China-exlusive promotions but because of the severely-restricted nature of their release we continue to class them as 'not implemented'. Hopefully they'll receive a worldwide release in the future!

Bluesky
Midnight
The War Within
Dragonflight

Preyhunter's Prismguard
Volatile Venomfang
Zesty
Snek'zali
Preyhunter's Riftbreaker