SCP Foundation

The big thing to watch out for would be higher order effects from the object's existence. If you introduce a galaxy-massive object in a galaxy, well, the gravitational effect will be immediately noted. Furthermore, an Earth-sized object, even with a halo, will be hard to see at interstellar distances (see how the exoplanet search is going).

Having the "potential to destroy a black hole" is guaranteed, if it's a galaxy-mass Earth-sized object. The Milky Way, itself, has a supermassive black hole at its center, and its mass is over 4 million times the mass of the Sun. Its Schwarzschild radius is about 10 million kilometers, so it's far larger than the Earth, and there's no way to measure the size of anything inside it. (Incidentally, the Schwarzschild radius of the entire Milky Way is about 0.2 light years, so it would dwarf the entire Solar System).

With that in mind, you're better off not thinking about it in terms of physics. You want it not destroyed by a black hole? It isn't. Your challenge is then just making the fiat work while maintaining suspension of disbelief.

ETA: What you're essentially describing is a naked singularity. Do some reading there, see how it affects what you want to do, and we can build from there.

Good idea, I'll go ahead and take a look at a few.

I might go ahead with that when I get around to writing my SCP up.

One of the issues with black holes, as far as I can see, is that we can't tell weather or not it destroys a black hole. If it functions similarly enough, it'll "absorb" the black hole, adding the black hole's mass to its own.

Hell, turning it into a black hole with a mass greater than what's in the observable universe is enough to classify it as a SCP. Throw it in as the Great Attractor and origin of Dark Flow, with it being functionally equal to a drain in the universe, and well…