The following fiends can be unlocked by capturing the same types of species and creatures.
Fenrir
Unlocked by capturing three of each Wolf/Lupine-type fiend.
Ornitholestes
Unlocked by capturing three of each Reptile-type fiend.
Pteryx
Unlocked by capturing five of each Bird-type fiend.
Hornet
Unlocked by capturing four of each Wasp-type fiend.
Vidatu
Unlocked by capturing four of each Imp-type fiend.
One-Eye
Unlocked by capturing four of each Eye/Bat-type fiend.
Jumbo Flan
Unlocked by capturing three of each Flan-type fiend.
Nega Elemental
Unlocked by capturing three of each Element-type fiend.
Tanket
Unlocked by capturing three of each Helm/Armored-type fiend.
Fafnir
Unlocked by capturing four of each Drake-type fiend.
Sleep Sprout
Unlocked by capturing five of each Fungii-type fiend.
Bomb King
Unlocked by capturing five of each Bomb-type fiend.
Juggernaut
Unlocked by capturing five of each Ruminant-type fiend.
Ironclad
Unlocked by capturing ten of each Iron Giant-type fiend.