A lot of freshmen were stunned.
Because they weren't able to discern that a ghost was even there. They didn't sense any form of energy fluctuations. They couldn't sense the energy of death and dark element from the challenger.
Of course, the black cloak could have been a giveaway. At least, it made sense to them now.
They all felt chills run down their spine.
The challenger is a necromancer. Most of the time, necromancers are easy to spot and it is easier to anticipate their attacks. Because more often than not, all of their attacks come from their undead. They have to send a command to the undead which in turn will attack.
That is also one of the major drawbacks of the necromancer and this prompts them to work from behind the scenes.
However, out in the open, this necromancer defeated people and he used the same move again and again. Until someone destroyed the move completely, they weren't able to even find it.