Lady Jaina Proudmoore

With the recent skip added to Jaina, this mount will considerably be easier to farm for both guild groups and pugs. As the article says, you need to have killed Jaina at least once before to unlock the skip, but fails to mention that only one person needs to have defeated Jaina is enough to bring everyone in, including people who never stepped foot in the raid before. The skip unlocks account-wide as well, so you can skip with your alts to give you extra chances at the mount.

After trying to get this mount myself, I've found out about the cheese/no interrupt strategy. Whether you're in pug or a guild group, this is worth checking out:

Before you pull the boss

1. 
   
2. Mark one range DPS and one melee DPS/tank. Make sure ranged stay grouped together for the first phase and then everyone should move in as a group during the intermission. You need to be stacked with at least 5 other people at all time due to [spell=289379], with the exception of people running out with [spell=287585]. If you're pugging, it is ideal to grab at least 8+ melee DPS/tanks and/or 8+ ranged DPS/healers so that people don't get frozen. You can also assign some ranged to stack on boss if you don't have a lot of melee DPS.
3. 
   
4. Ask people to take off their interrupt spell off their bar. This isn't required, but may avoid a silly wipe where someone interrupts the boss by accident. If you have a protection paladin in your group, [spell=31935] will also interrupt so make sure your tank does not use this spell on Jaina (or at all) during the intermission.
5. 
   
6. You need a fairly good amount of DPS for this strat to work, especially in pug groups where most people don't know the mechanics. If you're pugging, having 460ilvl or higher is a safe bet for this fight, but you can go lower. Ideally you can push the boss fast enough to skip the first [spell=290036]. Do not cast Bloodlust/Heroism or similar spells in the 1st phase. This will make Jaina uses Ice Block like any good mage would do to avoid dying, making her immune to any damage for 20 seconds. However, there's yet another cheese alternative where a leatherworker can use their Tool of the Trade, [item=164978], which won't trigger Jaina's Ice Block, which is worth using in the 1st phase if you need extra DPS.
7. 
   

Phase one: Burning Seas (boat phase)

1. 
   
2. Run out of the group with [spell=287585], then quickly stack up with your group so you don't get frozen.
3. 
   
4. Avoid getting hit by [spell=285828] and [spell=285177] by moving as a group and avoid walking on the [spell=287365].
5. 
   
6. Ranged should be breaking people out of ice blocks if they see any.
7. 
   
8. When the boss is getting near 60%, everyone should stack up.
9. 
   

Intermission: Howling Winds (blizzard phase)

1. 
   
2. Everyone should be stacked due to [spell=289379]. Before you jump off the ship, make sure you break people out of ice blocks and res anyone if needed. Then everyone jump down the ship together.
3. 
   
4. As you're walking down the ice platform, try to hug the left side of the wall and follow the marked people in your group. Don't hesitate to slow down to avoid leaving anyone behind, you don't need to quickly reach the boss anyway.
5. 
   
6. If you start having high stacks of [spell=285212] (>15), intentionally hit the [spell=288325] that run by your group to get frozen, which will drop your stacks (isn't necessary if you have good healers).
7. 
   
8. Keep hugging the left wall, killing the [npc=149535]s on the way, until you reach Jaina.
9. 
   

At this point, if your group was fast, Jaina will be uninterruptible, and she will have [spell=282841]. Melee can start stacking on the boss and ranged should be right behind them. Melee will get hit by most of the [spell=288325] that come off the boss and ranged will have to cleave the Ice Blocks down. Hold off DPS CDs until the boss becomes interruptible. DO NOT INTERRUPT THE BOSS, or the strat will fail. From there, Jaina has no more shield and you can DPS her down. You can safely cast Bloodlust/Hero (if you didn't use the LW Mallet) and the boss won't Ice Block (if she does, that means someone kicked her). You won't have to deal with the last two phases and the second intermission with this strategy, making the fight nearly trivial to complete.

Worth noting that Legion had an old system for the [item=137575] and [item=152789] mounts, where it used to be 5% drop chance per person in the group, up to 100% drop chance for 1 person with a full 20man group. However, after doing 4-5 kills with around 15 people (or less) in my group, Jaina always dropped two mounts, prioritizing people who didn't already had it. Based from my own personal experience, I'd say it's a safe bet to bring less than 20 if your guild can avoid pugging, or if you want to increase your chance at getting the mount (if you can still have enough DPS to push the boss fast enough), but there's still no official post that confirms whether or not that system is still in place. And as usual, the drop chance of the mount will be lowered to around 1% when the expansion is over, like how it used to be for Legion and WoD's Mythic raid mounts.

Good luck!

I made a video using Hyrcyne's strat, you can see it here: https://youtu.be/GkYgbIaqvQY