Terror Birds have 9 physical mutations, 4 of them are Mane Mutations, 4 are Tail Mutations and the last one is the Fangs Mutation.
While it is possible to combine a Mane and a Tail Mutation, it is not possible to have two or more Mane / Tail Mutations at a time!
 
The Fangs Mutation can only be inherited from Assur, the Goddess of War and Fury or from other Terror Birds having them. They cannot be chosen for any type of custom!

Standard Mane and Tail:

Special Combination Silkie:

Silkie works just like Sleek for Sabers and Dire Worgs. If a Terror Bird chick inherits the Silkie Mane it will automatically gain the Silkie Tail on top. Is it the other way around, the Chick inherits the Silkie Tail, it will not get the Silkie Mane on top though!

Mane – Crested:

Mane – Razor

Mane – Sideburns:

Tail – Bobtail:

Tail – Butterfly:

Tail – Long:

Misc – Fangs:

Fangs can only be passed down from Assur or other beasts having this Mutation. It cannot be chosen for Semi-Customs.