One is a mobile floating weather factory dripping rainbow, and the other is a mobile floating zombie factory dripping poison slime.

I’d compare it more to Dalaran in Northren but maybe that’s just me.

I was cast out by my comrades. Exiled. Forced to wander the frozen waste.  
But I was not alone. Not entirely. The voice, now my only companion, guided me to my destination.  
Strange, nightmarish creatures awaited me at the entrace. I felt my blood run cold, as cold as Icecrown itself.  
Inside, I witnessed horrific actes. Demonstrations of power. Power that could be mine for the asking.  
Terrified, I ran. But I did not get far.  
All too soon, my choice was made. Too lated did I realiaze that such power does not come… without a price.
 
Now, the world will pay a far greater toll. For I have returned.  
I am Kel’Thuzad.  
Your curiousity will be the death of you.

the difference is rainbows. duh.

Meld the two in fanart.
 
Or of them both dealing with airway traffic.

Cool!