Creating a array of custom objects from JSON, sent using PHP from a MySQL database
Let me try to clean it little bit.  

1 First of all you made jsonArray global. I think it's not necessary.
You can declare it locally where needed.

2 retrieveData() function looks very messy.
You can abstract that creation of Blog object.

3 You can improve for loop code

So here is what I would propose:

class Blog: NSObject {

  var blogName: String!
  var blogStatus1: String!
  var blogStatus2: String!
  var blogURL: String!
  var blogID: String!
  var blogType: String!
  var blogDate: String!
  var blogPop: String!

  init?(from jsonObject: AnyObject) {
    guard let bID: String = jsonObject.object(forKey: "id") as? String,
        let bName: String = jsonObject.object(forKey: "blogName") as? String,
        let bStatus1: String = jsonObject.object(forKey: "blogStatus1") as? String,
        let bStatus2: String = jsonObject.object(forKey: "blogStatus2") as? String,
        let bURL: String = jsonObject.object(forKey: "blogURL") as? String,
        let bType: String = jsonObject.object(forKey: "blogType") as? String,
        let bDate: String = jsonObject.object(forKey: "blogDate") as? String,
        let bPop: String = jsonObject.object(forKey: "blogPop") as? String else {
            print("Error: (Creating Game Object)")
            return nil
    }
    blogName = bName
    blogStatus1 = bStatus1
    blogStatus2 = bStatus2
    blogURL = bURL
    blogID = bID
    blogType = bType
    blogDate = bDate
    blogPop = bPop
    super.init()
  }
}


So outside world will not have to worry about converting json object into Blog.

Then simply use this abstraction as:

var mainArray = [Blog]()

func retrieveData() {

  let getDataURL = "http://example.com/receiving.php"
  let url: NSURL = NSURL(string: getDataURL)!

  do {
    let data: Data = try Data(contentsOf: url as URL)
    let jsonArray = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as! NSMutableArray

    // Looping through jsonArray
    for jsonObject in jsonArray {
      if let blog = Blog(from: jsonObject as AnyObject) {
        mainArray.append(blog)
      }
    }
  }
  catch {
    print("Error: (Retrieving Data)")
  }
  myTableView.reloadData()
}