It's a couch made of paper mache. I get in, and stalk you.

 

I run over the next user with a train, while tied up in chains, unconscious.

The train derailed because you couldn't drive it as you were tied up in chains, unconscious. (The subject in that sentence is 'I').

 

I force feed the next user Potassium of Cyanide.

@iamdumb!

 I break it down and throw away the pottasium and the cyanide

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The next person is stuck in a box made of an unbreakable box of a future material called unobtanium with only carbon dioxide , no oxygen:D I won!

Fortunately, it turns out that unobtainium is extremely reactive with mercury. So I simply poured some mercury onto the floor of the box, causing the unobtainium to crumble into a very fine powder, which I moved out of the way before escaping through the hole. All of this took place in thirty seconds, which is not long enough for the CO2 atmosphere to have any effect.

 

The next user is trapped in a teflon box full of fluorine gas which immediately sets them on fire.

I'm unfortunately a diamond, so the fire doesn't actually do anything to me. Also, I can stay in the teflon box for several hundred million years to come. By that time, the teflon box would break under the pressure of the heavy soil, and whatever lifeform would live on Earth would have detected the teflon box's presence long ago, take advantage of this and dig me out. I'm now displayed in an alien museum.

 

The next user is trapped in a reinforced chamber full of WARP.

Unfortunately, I'm also a diamond, so the WARP does nothing to me.

 

The next user falls into lava

I was wearing magic boots from the MC special armour mod, which turns lava that you step on into harmless obsidian.

 

If the next player survives this attack, they will die.

i am a stone block. which is, a dead thing. how can dead things die?!?!?!

the next user was caught by that paradox.

I am Doctor Who. Or kronos the titan lord of time. People are a bit hazy on that.

 

The next user is force-fed 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 full-size RITZ crackers.

I am a black hole. I ate all of the crackers, expanding to the size of a large galaxy, before collapsing the universe and creating a new big bang.

 

The next user is a normal human who is trapped in the collapsing universe, with no way of escape, including wormholes and Dr. Who.