Undead Battler of Northrend

Beegle Blastfuse:

Fragment of Anger: 1/1/2
Fragment of Desire: 2/2/1
Drowned Hatchling: 1/1/1

Against Dinner:
1. Use Spirit Spikes
2. Use Spiritfire Beam
3. Use Spiritfire Bolt
4. Use Spiritfire Bolt
5. Use Spiritfire Bolt
6. Use Spiritfire Bolt again if needed

Gobbles comes in
1. Pass as you will get put to sleep
2. Pass
3. Use Spiritfire Bolt
4. Use Spiritfire Bolt
Fragment of Anger should die here
5. Spiritefire Bolt again

Use your Fragment of Desire against Warble:
1. Use Soulrush
2. Arcane Blast
3. Arcane Blast
4. Arcane Blast
5. Arcane Blast
Win! Drowned Hatchling was not needed in this fight. Please note that the opponent's moves seemed very unpredictable in this fight. Improvise if needed with the listed pets, but it should usually be a 2-pet-fight.

Okrut Dragonwaste
Scourged Whelpling: 2/1/2
Blighted Squirrel: 1/1/1
Ghastly Kid: 1/2/1

Against Drogar:
1. Use Call Darkness (if Drogar flies up on the first round, restart)
2. Use Tail Sweep
3. Use Tail Sweep
4. Dreadful Breath

- If your Whelpling dies here and goes into undead round with Drogar being low: Dreadful Breath again to finish him off (this is what happened to me in 2 of 3 restarts)
- If you managed to double cast Dreadful Breath without dying:
Use Call Darkness in your undead Round against Sleet.

Against Sleet:
Your Blighted Squirrel enters
1. Scratch
2. Scratch
3. Scratch
4. Sleet goes into Undead Round: Use any ability or pass, I used Rabid Strike

Against Rot:
5. Scratch
(Squirrel should die and be stunned in its undead round and not be able to cast Scratch)
Ghastly Kid enters
1. Hoof
2. Hoof
Rot should die here
3. Ethereal
You win - Please note that the opponent's moves seemed very unpredictable in this fight. A win should be guaranteed, you just have to improvise again if the opponent's moves differ from this post.

Nearly Headless Jacob:
Blighted Squirrel 1/1/2
Infected Fawn 2/1/2
Scourged Whelpling 2/1/1

Against Spooky Strangler:
1. Adrenaline Rush
2. Stampede
Scourged Whelpling enters
3. Call Darkness
4. Pass in Spooky Strangler's undead round

Switch to Infected Fawn to fight against Stitch
1. Adrenaline Rush
2. Flurry
3. Flurry
4. Flurry
5. (Flurry again if needed)
Stitch dies
6. Adrenaline Rush

Mort enters
1. Flurry
2. Flurry
Infected Fawn should die here
3. Flurry again in Infected Fawns undead round

Bring Scourged Whelpling In
1. Call Darkness
2. Pass
Win!

Gutretch
Irongrasp 1/2/1
Son of Sethe 2/2/1
Cursed Birman 1/1/1

Against Cadavus:
1. Black Claw
2. Metal Fist
3. Metal Fist
4. Metal Fist and you die
5. Metal Fist again your undead round

Son of Sethe comes in against Fleshrender
1. Plagued Blood
2. Touch of the Animus
3. Drain Blood
4. Plagued Blood
5. Plagued Blood
6. Plagued Blood
7. Touch of the Animus (Personally I made the mistake of using Plagued Blood here instead, so I had to improvise. It's not that big of a deal and as I found out it certainly works, too)
Fleshrender dies

Blight enters:
8. Drain Blood (you die)
9. Plagued Blood in your undead round

Cursed Birman comes in
1. Call Darkness
2. Pounce
Win!

Major Payne
Irongrasp 1/2/1
Ghostflame 1/1/1
Severs 1/2/2

Against Grizzle:
1. Black Claw (you get stunned)
2. Pass
3. Black Claw
4. Metal Fist
5. Metal Fist
6. Metal Fist
7. Metal Fist
Grizzle should die here

Beakmaster X-225 enters
8. Black Claw (you die)
9. Metal Fist

Your Ghostflame enters
1. Seethe
2. Seethe
3. Seethe
Beakmaster resurrects
4. Seethe again

Bloom enters
5. Breath of Sorrow

Severs enters
1. Squeeze
2. Grasp
3. Grasp again
Win with around 30% HP left.

I completely improvised all the strategies listed above. There is certainly still room for improvement in the efficiency of the strategies.

I also mentioned that the first two battles are very RNG-heavy. I'd like to point out that this can apply to the other three pet battles aswell as I only restarted the first two fights of this post several times.

Undead

For all EK, Kalimdor and Northrend Family Battlers - Undead I used the same team

Blightbreath (Dreaful Breath, Any, Acid Rain)
Fragment of Anger (Seethe, Spiritfire Beam, Soulrush)
Zomstrok (Infected Claw, Any, Carpnado)

I used Acid Rain into Dreadful Breath as much as possible. When Blightbreath died, I used Spiritfire Beam, then Soulrush > Seethe. When Fragment of Anger died, I used Carpnado to clean up whatever was left. Most of the time I didn't need the Zomstrok.

When I vs'd Major Payne, I started with Zomstrok instead then immediately swapped to Blightbreath once stunned. Focus all your big damage abilities on the bear.

As you might have noticed, as of Patch 12.0.0, you can only challenge the Pet Battles Trainers in Kalimdor, Eastern Kingdoms and Northrend once per day.

Which means that for the new meta achievements being introduced with Midnight's Pre Patch, it will take a minimum of 10 days to complete (one day per pet family).