The Alliance of Terror is a group of powerful and dangerous people that B/N will form, human or monster alike. 

And this could be a fitting theme for them:

https://youtu.be/W-zbYkTOCmM

B/N: Leader of the Alliance. His goal: No world domination or total destruction, his goal is to prove his absolute dominance of all the others. Everyone who's stupid enough to stand in his way, shall suffer the consequences.

Infinte: Also known as Zero the jackal. B/N's right hand. Master of illusions and despair thanks to the phantom ruby. His goal is to prove his strength over all, no matter what. (He's not weak)!

Dabi: Also known as Touya Schnee. The eldest son of the Schnee family who was presumed to be dead to everyone in the Kingdom of Atlas. His goal is kill his family and destroy Atlas. 

Uka-Uka: Evil mask and brother of Aku-Aku. Contains alot of evil energy and magic. Even he joins forces with B/N, who is much more worthy than Cortex was, he's still after world domination.

Kuroka: A Nekomata Faunus who wields both demonic power and Youjutstu, revolving around the manipulation of Youki to cause various effects ranging around. 

Gigan: Cyborg Kaiju. Equiped with tons of deadly weapons. A heartless machine, who kills everyone in his way.

Destoroyah: Mutated Kaiju. Got the ability to destroy oxygen around a great area. A brute and deadly monster.

Dr. Robotnik A.K.A Eggman: A mad scientists who creates robots and drones to do his bidding and follow their programming.  

Kagura: Also known as goddess of destruction. A master of spatial manipulation and distort reality. Her goal is to causes destruction all over her enemies.

Naraku: Kagura's bodyguard. Even though Kagura is powerful, Naraku won't hesitate to protect in battle. she'll always be by her side, even if that means she'll join B/N's group.

Shiki: Part of a royal family, and user of the Yasakani Magatama. Merciless to enemys but still kindhearted. His his reason to stay in the alliance is unknown for now.

Alarak: Highlord of the Tal'Darim, Alarak is one of B/N's deadliest allies who won't show mercy to his enemies. 

Rahzar: Once a human who was a world famous martial artist, before he mutated into a near-skeletal gray werewolf with some gray razor-sharp bones exposed, Rahzar is a fearsome warrior. 

Indominus Rex and Indoraptor: B/N was able to create two fearsom dinosaur hybrids. These hybrids are much stronger than any other dinosaur, deadly and high unpredictable. But still they are following any order of his creator.