Killing a mouse is the tamest test of evilness that I've ever heard.
Well, I think it was significant that Our Hero simply lets go of the mouse, dropping it in the tank. He has no clue as to what's in the tank, and therefore no clue that it will harm the mouse any more than getting it wet. The applicant at the end (I think) holds the mouse in his fist (already being a bit more aggressive) and holds it underwater until it dies, which is considerably more Evilish. I guess it's a hint that Our Hero is not as evil as his students, at the end.
Cats, and to some extent mice, being small cute furry critters that can be pets, serve as surrogate children. Just ask any childless couple whose dog or cat is killed. I suppose that because mice are usually regarded as vermin and cats are usually pets, the cat crucifixion is an escalation.
I had a bit of trouble figuring out what was going on between the tornado and the appearance of the Traveller, because at 17:01 (of the copy I downloaded) it sounds like a vital piece of the recording was clipped out, and I had to replay it several times before I figured out that the Traveller had arrived at that moment. That took me out of the story.
While I was listening to it, it was only by sheer strength of will that I did not just skip to the next episode. The ending made up for it somewhat, so I give it a 5 out of 10.
The twist ending reminded me of an old story that went the opposite way. It was in an annual anthology back in the '60s, I think. Our Hero is a disenchanted young adult who plots to assassinate an evil dictator who is going to visit his small town on a whistle-stop tour by blowing up his limo. The bomb is "nullified", the motorcycle-riding bodyguards zap him unconcious. When he wakes up in some holding facility, they convince him (and the reader) that the dictator dude is really quite okay. The Hero is made to "disappear" on paper so as to serve as an example to other would-be terrorists, and is invited to join the Dictator's staff. The story ends with Our Hero riding a bike in the motorcade, wearing a full-face tinted visor helmet so that he cannot be recognised. They recruited all their security staff from the would-be terrorists that they encountered on a regular basis, and the tours were a way to bring them out into the open. (I wish I could remember the title, it was something like "Day of the Bad Man".)
But for someone who wants power in order to dominate others, why would they even agree to join a course where none of the students were ever heard of again? If I was going to evil wizard school, I'd want to go to the one which has the most alumni that are still talked about only in scared whispers.
That did seem like a bit of a rhinoceros in the living room to me. We also are not given any hint as to what kind of power they were supposed to be getting, and why it would be cool to have. There was little motivation for the main character.
One more thing. "Adrian"? Was that his real name, or did he google for "evil acolytes proper noun"? I guess it could have been worse, something like "Damien".