It's a Box.

Boop. Every commenter opens a mysterious box that you can obtain magically from this thread and announces what's in it.
Let's pretend the box has infinite space and physics inside, so you can pull out anything like a cookie or Vanaduke or an alternate universe.
Rules?
1.) Open a box and say what's in it.
2.) Only the next player can specify what happens to the contents, then opens a box.
3.) The action has to affect at least one player or all players.
Extras?
1.) Everybody has infinite lives or bans, so you're not out if you die or something.
2.) Try your best not to repeat contents.
Example?
Player 1: I open a box. It has pants in it.
Player 2: The pants catches on fire for being a liar and burns Player 1. I open a box. It has a banana in it.
Next commenter:
Etc. Let's begin
I have opened a box. It's got The Arcade forums in it.

So basically a sortof reverse Give the Surprise?
The protonium explodes.
I open the box and get some cheese.

I actually didn't know about that Give The Surprise thread, since I'm not here very often.
The cheese knocks out Matik and Pi with the stench. I use it to make some soup and leave it in the forum thread.
I open a box. It's got Matik's right arm in it.

The right arm was actually armed with a laser cannon, which blasts Teddysmacker's face.
I open a protonium box. It has a legendary chaingun.
The Chaingun was actually a huge bomb
I open a cuteness box and 99 Kittens fly out

Bay at suffocates with the kittens all over him.
I open a cardboard box. It has a live flamingo in it.
The flamingo Explodes
I open a strange box and a fat penguin comes out

The fat penguin mistakes Baycat for a pink blob and hits them with a hammer.
I open a box and find another box.

Crazee-Pi faints from the universal problem with this. Or something
I open that box and find a Flintlock, loaded with one lead ball.

The Mario Maker turns you into a Goomba.
I open a nanobox and I find an Unheatable Proto Sword of +999 Shame

Then you realize that it's a Proto Sword and literally anything would be better than it.
I open the box and find a box. I open this box and find a box.
This is probably going to last a while.

Ze-Epik dies after opening boxes for his lifetime. We bury him in a mansion-size coffin that we made out of the box remains.
I open a box and find a bar of soap.

Teddysmacker drops it.
BAD END.
I open up a box... and finds a snake inside [!]

I yell: "Snake respond. Snake? SNAAAAAAAKE!" The snake died.
I open a box. And find cheese pizza.

Blazecat ate the cheese pizza.
(noo i wanted that)
I open a box and find a 300x times big Earth.

An omnipotent author then writes Markelu out of existence for rebelling against said author's conscience.
I open a box... and I find all of the world's evils inside...

I close the box. It's too ugly.
I open a box. It has a live flamingo. No wait I did that already.
It has a Bubble Gun, with a silencer, 6x scope, and a laser sight for flair.

Blazecat goes full genocide and tries to kill everyone, but then realizes it's a bubble gun, and then jumps off a cliff to end his misery.
I open a box.
It has air in it.

Turns out the air in that box had a lower than normal oxygen concentration, which causes Markelu to promptly pass out.
I open up a box, and inside I find... a scale model of the aircraft carrier Shoukaku?!

The aircraft carrier model randomly inflates to full size and crushes Delecated.
I open a CRATE, and find a note telling me to use boxes instead of crates.

Alongside the note, Ze-Epik finds an UNUSUAL HAT!
The WEALTH and STATUS he gains is enough to convince the COSMIC RULES POLICE to call off his arrest!
I open up a box, and I find... a rather large tongue?
Wait, why are the insides of the box flaps lined with teeth...?

The box-mouth suddenly eats Delecated.
I open a box. Inside the box, is a trade offer to buy my Unusual Hat.

For some reason, Ze-Epik sells the unusual hat for 1 scrap.
I open an imaginary box. I find a black hole inside.

The black hole starts charging energy.
It becomes miniscule.
It says: "Kame-hame-HA" and explodes and destroys half the Earth.
You also lose the coin.
(...did you get the Kurzgesagt reference?)
I open a lockbox. It has an assortment of cosmetics inside of it.
You decide to sell those cosmetics in Auction House. You get a lot of money, so you buy some accessories and sell them again. Then, you buy a fancy costume for yourself. Congratulations! Now you're one of the Spiral Knights trading elite. Unfortunately, that means you won't be able to really play the game again because you'll be standing in front of the Auction House all the time.
I open a box. There's enough polygons inside of it.

Then you realize that your N64 is in fact not an N64, it's a SNES.
And the Super FX chip fell out.
The universe crashes.
I open a case and find a weird-looking wrench that has fire coming off of it and it looks super shiny.

Now lacking the WEALTH and STATUS to convince them otherwise, Ze-Epik gets arrested by the COSMIC RULES POLICE for opening a Case instead of a Box.
I open a box and inside I find 200 5.56mm bullets uniformly chained in a long belt. Is this some sort of lame pun?

The Heavy then comes along, punches you in the face and reloads his minigun.
(vote 4 Ammo Rezerv to be put in TF2 today)
I open a box to see an identical clone of myself.

The identical clone promptly stabs Ze-Epik and goes on living as him, without anyone knowing or suspecting anything.
I open a box. It contains three boxes with question marks and a post criticising the game for not having the boxes change anything.
The post gets criticised by other ones.
I open a box, containing a dead meme.

"ONE DOES NOT SIMPLY
RECEIVE A DEAD MEME"
I open the box, it contains an angry horde of pirates.
Crazee is attacked by the horde of pirates and thrown off deck (yeah they're on a ship now), promptly drowning.
I open the box and find a necroed post.
Teddysmacker gets crushed to death by new forumers.
I open a freaking box.
It has protonium in it.