Rush the elf. With everything you have. Assuming you scouted this fast enough you should be able to hall him. NE probably has nothing (lots of lumber feed required for an immeditae tech) and UD only has a couple of ghouls, max. If you're desperate enough tower him.
If u manage to hall the NE, the game is pretty much over.
This strat is not as effective in 2s as it is in 3s though.