Hajime's feral instinct might reflect his true identity as Joker, the wildcard.
Leangle actually seemed to get stronger after the Spider Undead was sealed the second time, even though he didn't get a stronger form. Why? The Catagory Ace had an influence on him because it wasn't sealed correctly the first time, after being sealed correctly, the system could fully use his powers.
There's a couple situations that seem to be deliberately ironic reversals of things seen last year. In Faiz, the Riders were the doing of the original, good leader of the evil organization. In Blade, the Riders were the doing of the original, evil leader of the good organization. Also, in Faiz,Poor Communication Kills. In Blade, the Monster of the Week impersonating Riders to sow discord is resolved very quickly by the characters checking with each other and assuming the obvious. In Faiz, the cast would never dream of doing that, and such a situation would've resulted in everyone hating each other for ten episodes, surely. Don't know whether that's an affectionate nod or a Take That!.
Given that the guy who wrote the episodes with the Monster of the Week impersonating people is the same person who wrote all of Faiz, it's possible that it's something of a Self-Parody.
Why does Kenzaki have an unusually high fusion coefficiency? Because the Undead are meant to be warriors fighting solely to protect the future of their species, and Kenzaki's mindset of gaining power for the sole purpose of protecting others matches this perfectly.