Here is the full list of all 16 Mega Serval achievements.
Save Black Jaguar!
Save Japanese Crested Ibis!
Save Common Vampire Bat!
Save Grey Wolf!
Save Margay!
Save Blackbuck!
Save Western Parotia & Greater Lophorina!
Save African Rock Python
Clear the amusement park at the foot of the mountain!
Survive the cerulean-infested hotel!
Pass through the secret research lab!
Save her!
Find one rainbow ramune!
Find all eight rainbow ramune!
Find a consumable potion!
Defeat Black Jaguar with her own ability!