The Powder Toy

5/10 Borrows a time machine   Arrives in Hiroshima one second before the nuke explodes.

I just restart the computer.   !set type next user AMTR.

However, the sound is of such a low frequency that I don't hear it.   The next user is buried alive under one hundred feet of solid ice, in the middle of Antarctica, with no way to escape.

I simply eat the bullet since I'm still a black hole.   The next user is trapped underwater next to one of SCP-118's assembly areas.

6/10 Decides to lose weight using weightloss pills.   Explodes, since the pills contained antimatter.

If such a wall were implemented, it should also be useful in preventing ambient heat from travelling into areas where it is unwanted.

I simply live the rest of my life as a black hole.   The next user is falling through my event horizon.

6/10 8/10 Finds a $100 bill.   It's Confederate money and therefore worthless.

Fortunately, the room's walls were made of reflective material, so the sculpture remained still.   The next user is slowly being turned into a blob of neutron star matter.

As in electrolyzing it like how ELEC electrolyzes WATR.