Completely disappeared without a trace. And deserters, who should have been brought back from previous installments of Heroes.

And if you add some azure creatures here, it will be even more intense! Maybe even some divine messengers? Azure creatures can even defeat a summoned phoenix like it's nothing! It's already quite tough, and there are many cool creatures, so there's no need to add more blue ones.

Added 2 minutes later
You're right about the efreets. Nagas are already being replaced by rakshasas, and if you create a new creature for each unit with four arms, it will look ridiculous. Heroes 5 already has enough arms! We definitely need to bring back the monsters, and also the werewolves. What about cyclops? They can be one-eyed. And if you don't make a swamp, I'll start haunting your dreams!