Sorry, I don't know how to name it properly, but those "mis grid objects" are wall, door, region and background objects that have height and width less than 10.
Here is a good example of a map using these objects (zzninjazz-christmas):
To create them all you have to do is to download the xml file of your map, edit object's dimension using notepad, and then upload it back to Plazma Burst 2.
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Now step by step, let's make this wall smaller than 10 pixels height.
1. First we add this wall in level editor and save the map.
2. Now we download and open the map xml file in notepad. Let's find the wall we are editing through it's coordinates (X=-300; Y=-710). Here it is:
3. Let's change the height of the wall to 5, press "save", and upload the edited xml file back to Plazma Burst 2.
4. Now let's check if it worked by opening the map in level editor. Yep, it works.
Note 1: You cannot copy-paste these objects in level editor.
Note 2: You cannot move these objects in level editor.