Monster Allergy/WMG

Zick didn't lose his powers.
I get a feeling that he still has his powers in the end of the comic and it would be reactivate once there is danger.

The townspeople can see the monsters all along.
It turns out that hidden in some townspeople are Monster Tamers and Keepers. They have to pretend they didn't see the monsters to keep the Masquerade going.

Bibbur-Si is the modern day version of the Shinigami Realm.
After he went back to the Shinigami Realm, Ryuk has followed Light's instructions to make the realm a better one. He orders the Shinigami to build their realm around the skyscrapers of Bigburg and that is how Bibbur-Si is created.

On the top of that, the Gift of Sight is the modern day version of the Shinigami Eyes. The difference is that when getting it, there is no decreasing half of the individual's life span.

Elena is in the coma and that the entire show is a dream.
When she goes to Zick's house and screams at seeing Zick himself, she suddenly fainted. The thing about her seeing invisible monsters happens to be a dream itself. By the time she gets the Gift of Sight, this is just projected on her mind.

Gorkas are aliens, not monsters.
Well, they have a third eye on their foreheads and this is one difference with the evil monsters. This proves that they're are aliens from outer space.

Elena is a monster all this time and being human is only her transformation.
The reason of why she can't see the monsters is because her powers of seeing them are drained when she was born. What else is that she is turned human and loses her memories, making her think that she's a human. When Greta granted her the Gift of Sight, it seems to activate her monster status and regain her memories.

Everyone is in the Reaper's Game.
The contestants are the Tamers like Zick, Teddy, and Lay. Their goal is to achieve of their missions of getting back to the RG.

There's also the Support Reapers and it's the Keepers, the ones whose only power is seeing monsters. Elena and Greta are examples of this. Addition to this are the Tutors and their types (Stellar and Maximum). Timothy, Lardine, and Jeremy are under this.

Now as for the Reapers, Magnacat is the Composer for season 1, while Omniquad and Omnised are Game Masters, respectively. When there is season 2, a new game comes with Moog Magister becoming the Composer, Emily Vermeer is the Game Master, and Hector Sinestro being the Conductor. The Harbingers are the Androgorkas, the Anguanes, Patty and Mattie,

Greta was giving Elena a Secret Test of Character from the beginning of season 1.
Think about it. When Elena discovers the world of monsters, she can't see them. All that Greta did was to make sure if she is ready to face the dangers around her. It would appear that by allowing herself to rescue Zick was the thing that made Greta convinced to get Elena to finally see the world of monsters.