So... Shocker just instantaneously conquered this one random city for no reason? No intrigue, no buildup, no resistance, just "SHOCKER NOW OWNS IT DAILY COMBATMEN PARADE IN THE STREETS"? You might have wanted to wait to discuss this post with your Co-GM really. This is kind of... well, it just feels awkward and restrictive.
Okay, I didn't explain pretty much anything yet about the plot yet on purpose. But...let me tell you what I had in mind: The city wasn't exactly random, it was built on the same place the seal was made 100 years ago, it happened to be the first place they appeared, and since it is a big and important city, why not dominate it? Now, about the abducting, they are raising their numbers by transforming the citizens in monsters of all sorts, spread them across the land until the planet is entirelly filled with them.
On the other hand, you are right, I should have discussed this and I appologize, I'm new to being a GM, so as I said in the Interest Check, I will commit mistakes and I appologize for that, please be patient with me.