I assume Monster falls under any creature created from the magic Ben brought to humans. Either Wade wasn't there as cleo sent all the students away or Fairies weren't created from the same source as the other monsters.

But isnt all magic from the magic ben brought?

We don't know if that story included witches or were just talking about about Monsters. Ben specifies that the magic he stole he gave to the villagers then the villagers tried to turn themselves into gods which resulted in monsters then Ben was cursed by the gods to have monsters attack him. Since witches didn't attack Ben it can mean they weren't apart of the villagers magic was given to. Or the writers could not have consider that or it could more to the story not yet explained.

In Not all those who wander are lost, Wade claims that he has been in therapy sessions with Emma. And as we have seen before Emma also uses therapy while physically making someone unconscious like a therapy box or Chamber de chasse or something similar to that. So, maybe Wade was in session while all this was happening. And so he couldn't attack Ben.

They probably use “monster” like “creatures that want to hurt or kill Ben”, but not in literal definition of “monster”, because vampires, werewolves and even witches should be classified as “monster” since they should have that magic and two of them was created using dark magic.

It's either Wade was just not at the school when Ben curse was active or his kind came after that curse was created. As vampires and Werewolves didn't exist back then. Witches(the Villagers) aren't really monsters, just humans with Magic.😎

Maybe it doesn't work on humanoid species,fairies may not be apart of the 3 main species but they're still human

@KnocknickKnock @Sean 175 Wade is Fairy not witch!

After reading all your comments, I concluded that either Wade had therapy with Emma for example at Chamber de chasse or was on a field trip with Finch. These are perhaps the two most sensible explanations.

I know, I just included them in trying to explain why they weren't trying to attack Ben as well.

Since fairies can do some magic (even bad at it) I believe they're a species derived from witches. Also, I understand that the monsters who attack Ben were created every time a human tried to use magic to conquer/slave others, like the Kroatoan, Mummy, Headless Horsemen or Gargoyles for example. Other monsters in Legacies seamed real species, like the tree in S01E05 and Jinnies (?) (the blue ones); that means, specially the ones who could do some kind of magic.