WHo could stop.....

The Spectre leaves Crispus and roams the earth freely, reaching his peak power. He is then commanded to again join to a mortal host, but this time of his choosing.

He picks The Man of Steel and Superman is possessed by the full power of the Spectre.

With Spectre's abilities cancelling Supes's vulnerability to magic, who in the DC universe can stop the Supes/Spectre on a full fledged rampage?

Captain Marvel w/Spear of Destiny

In the end the DC writers would somehow have Batman stop them

Black Alice.

All of the above are technically correct.

They wouldn't get a chance though, because Superman would reject the Spectre.

Also, I'm not sure adding Superman to the Spectre would add anything in the way of power...

Originally posted by Cogito

Also, I'm not sure adding Superman to the Spectre would add anything in the way of power...

Yea, to the Spectre the host is not a power boost, just a leash. Not like Eclipso.