Morty knows he shouldn't be screwing around with multidimensional shit. It's dangerous, it's impractical, it's blah blah blah. But it's a potential key to unlimited energy, how does nobody see that? He's built a dimensional siphon (it kind of looks like a cardboard box with a funnel and a TI-84 taped to it, but it damn well works), keyed in the dimensional coordinates to a random plane, and by God he's going to use it.
He flips the switch and waits for the energy bar to fill up.
It does! It fills up very rapidly. Then it explodes, along with the box. There's rather more smoke than there should be, and once the smoke clears someone is standing there.
"Oh my," Morty says faintly.
"Let's suppose that I would object to that. All right. Although I can look less human if it would help."
"This much," he says, demonstrating. Yellow eyes, snarly forehead ridges, fangs.
He starts off toward the Crystal Hall. "Most of the students who require blood can get by on synthetics, but if you turn out to be allergic we can get you a nice land mammal. Unless you need human blood, in which case you'll need to get acquainted with Xan."
"Is interacting with Xan very terrible? I don't need human, anyway, I can get by perfectly well on land mammals."
The teenager places a paper cup under a tap and pulls a lever, producing a quantity of blood which flows into the cup. Once the cup is mostly full the teenager caps it with a plastic lid, conscientiously tags the "blood" bubble on the "this drink contains:" section of the lid, and slides it over to Mark with a bendy straw. "Thank you, come again," he drawls.
"Thanks," Mark says cheerfully. He takes his drink and goes to locate Peter.
Peter is sitting with a young woman with strong facial similarities to someone Mark knows! She spots him and waves a fried drumstick of absurd size.