This may seem unorthodox, and I realize Lord Etch is evil, but perhaps we should ask him if he's aware of the GoLK. Since we're able to retain our memories in this world, maybe Etch will have some insight that we don't. As far as we all know, this is new to us, but Yoshi has apparently been trying to tell us about this menace for quite some time to no avail. His connection to The Oldest Orc seems to protect him. It's virtually impossible to fight an adversary that we can't remember and have no means of realizing even exists, but at least here we can form a strategy. I'm not entirely sure where we are, but I agree with Gareth in that there's definitely something more at play than a pocket universe. If it is some sort of prison or cosmic hiding spot for GoLK, then making others aware and spreading knowledge of it would be it's undoing. We just need to figure out how to do that while we still have the ability to remember things.
Note that Etch, unlike virtually everyone else you have encountered, understands your common and other languages you speak, so when do you say this?