What do?

[Qwertygiy]

You don't try to set game.World, at least I don't think so.

You need to switch the objects' parents to the other world.

For example,

[lua]
function changeWorld(p, w)
p.Parent = game:getWorld(w).Players
p.Character.Parent = game:getWorld(w).World
script.Parent.Parent = p
end

link(script.Parent.MouseDown, changeWorld)
[/lua]