SCP Foundation

SCP-x are to be contained in a standard humanoid containment chamber.

Even though you're referring to a group of humanoids, it sounds weird to use "are", so refer to them as one. That means no "SCP-XXXX are" and such.

By the way, are they kept in individual chambers? Might want to say that.

They are to be fed twice daily.

This sounds a bit abrupt. Maybe something like "Each instance of SCP-XXXX is to be fed standard rations daily."

Standard Site security measures for humanoids with telepathic communication are to be taken at all times.

I'm unsure about this. Maybe look at other telepathic SCPs and see how they're contained?

Personnel must read sheet SCP-XXXX-A-Laogmian, which contains SCP-XXXX's partially translated language.

Or we could try and teach them English, if they aren't hostile. Maybe have only a few people learn the language for interviewing?

Small comfort items, such as culinary mushrooms and cheese, may be given if good behaviour is maintained.

I wouldn't call then comfort items, unless they like to snuggle with mushrooms and cheese.

They vaguely resemble human infants with striped clothes of varying appearance covering their entire bodies except for their faces, although testing has revealed these clothes are actually part of their bodies.

This sentence is a bit messy. Try making it into two separate sentences.

They possess a varying number of tentacle-like appendages coming out of their heads.

That part about "coming out of the head" isn't good tone.

They possess the same physiological needs as human beings

I wouldn't use the word "possess". I would mash this sentence with the previous one, saying though they have tentacle things they still act like normal humans.

SCP-x are capable of telephatic communication and changing their body structure to generate new limbs and swallow objects that should not fit inside them

It's a run-off sentence, make this two sentences and elaborate a bit on both.

SCP-x-1 are the musical instruments used by instances of SCP-x.

They aren't exactly instruments, just describe what exactly they are.

They seem to possess a rudimentary intelligence and refuse to used by anyone other than instances of SCP-x.

How exactly are they utilized? And your missing a word in this sentence.

Come see wondrous critters that are ACROBATS and MUSICIANS at THE SAME TIME

I wouldn't say this. Why not point out their living musical instruments, and their "Death defying stunts" and "Spectacular musical talent"?

After falling, they seem to break their bones and then snap them back into place without making a sound.

The tone here could use some work.

which fly into the audience's faces while on fire.

Where'd the fire come from?

SCP-XXXX-17: It is our tradition to have a competition with visitors. But this time, they wanted not metal or harrzagumluboks, they wanted me and the others you have here. It was best out of three, like usual. First, music. We won, of course. Then came the dances, and Fular brought these tall guys made of wood with strings on them, and they won. On the last challenge, there was cooking, and by the Great Striped Ones Above, their food was wonderful. I'm… I'm sorry, I shouldn't talk well about them. I know they cheated some way! It was the only way!

This whole line of speech doesn't sound like the SCP that was previously talking, it sounds like a normal person.

Agent ██████: I am very sorry, but that is not what we do.

An agent wouldn't say this. It could agitate the SCP; we would give false reassurance instead.

Overall: I know English isn't your native language, and I can kind of tell in your writing. However, it certainly isn't bad, just sentences and stuff. I think the concept is cool, and the way you did it was good. Just seek more critique in chat maybe, to pick out the errors I missed, and this may do well.