Magical Mayhem

Alternate strategy for Gnasher:

P/P [npc=62914] 2/1/2 (Other breeds should work here, but you will probably need the backup pet because their damage throughput won't be as high)
H/H [npc=62317] 1/2/2
Whatever backup pet you want

1. Rake
2. Siphon Life
3. Leap
4. Rake
5. Leap
6. Leap - Twilight Fiendling dies, Minfernal comes in
7. Extra Plating
8. Crush
9. Crush
10. Explode - Gnasher dies, Win

Happy Achievement Hunting!

My team vs. Gnasher:

• 
  
• Viscidus Globule (1,2,1)
• 
  
• Trunks (2,1,1)
• 
  
• Twilight Fiendling (2,1,1) - didn't use
• 
  

Strategy by Round:

1. 
   
2. Start with Viscidus Globule. Poison Spit
3. 
   
4. Expunge
5. 
   
6. Ooze Touch
7. 
   
8. Poison Spit
9. 
   
10. (Globule dies - bring in Trunks)
11. 
    
12. Headbutt
13. 
    
14. Smash
15. 
    
16. Smash (Gnasher dies)
17. 
    

For [npc=128014], I finally managed to do it using the tips from Quenais over at Xu'Fu. Strategy requires Minfernal (sorry!).

[npc=71016]
[npc=62317]
[npc=61883]

1. Pass.
2. Extra Plating.
3. Crush.
4. Pass. Sapphire Cub gets swapped in.
5. Prowl.
6. Pounce.
7. Rake. An abyssal gets switched in.
8. Explode. Get in the other abyssal.
9. Explode again. Sapphire Cub is back
10. Pounce