I must say I have more interest in what the stock plant is than the red monster that's growing on it, I thought I might wait until it's a little more settled and then free it from the freeloader!
I saw somewhere you can cut a graft off leaving enough of the stock plant on the graft so that both can live?
The red plant might look nice if it's not waving about 4 inches off the ground.
There are a heap of mis treated plants out there, the only plus side is picking them up cheap when they're on their last legs and nursing them back.
So I'm assuming from your comment, the stock plant is a hylocereus and the red plant is a mutant gymnocalcium.
I'm a little more fond of the red plant knowing it's a gymnocalcium, I am a huge fan of that species!