So, my plot is a kind of children's myth/fairytale. Two grown brothers who have some sort of world-altering powers (never explained) who can build anything and can travel to any world, are approached for their aid. An ordinary man has asked the brothers to build him a new world.

They can't do it exactly to specifications, but the realize what they can do is share some of their power by creating a tool by which others can build worlds. However, a mysterious stranger is trying to prevent the project from being completed.

So far this stranger has managed to convince the original client to ask the brothers not to go through with the project, and has damaged the morale of the younger brother. The thing is, I still don't know *why*. Any thoughts? I like the basic story, but I need to know why the antagonist is doing this in order to figure out a resolution.

Okay... Why...

-The antagonist could be trying to enslave the people of the world and doesn't want them to create their own worlds.

-The antagonist could see in the future and see the destruction that will come of this machine.

-The antagonist could see the evil in people and just problems that will happen because of this.

-He could know that something in the machine willl be wrong and cause more problems...

That's all I've got right now. Hopefully it gets your wheels turning!

The stranger is from the future. The project caused horrible things to happen, so he is trying to prevent it from ever being completed.

Or maybe, the stranger is actually one of the brothers. The other brother was killed during the testing of the project. To stop this from happening, the brother that survived went back in time to try and save him.

I love your story.

My comments (without first reading what others have written):
1. He has a grudge against the ordinary man.
2. He wants to get the power for himself.
3. He just likes messing up things.
4. The new place is going to interfere with his own plans (for travel routes, mineral resources control, something).
5. He's jealous of the talents of the brothers and wants them to fail.

Hope these (somewhat pathetic) ideas help spark your imagination and get you to where you want to be.

Good luck.