I didn't see anyone who explained that yet so I'm going to do that once for all:
Creeper Nexus isn't in Map Editor because it's just a FAKE. I beaten Loki without Thor and I saw that he's just a part of the background!
You can see that at start of the mission too because the Creeper near the Creeper Nexus is very low.
I've explained it a few times.
_k
See here: http://knucklecracker.com/forums/index.php?topic=1018.0
And here: http://knucklecracker.com/forums/index.php?topic=2142.0