Okay, this is a quick read because I'm swamped in requests and this fell to page 4 with no replies. Here are my thoughts:
First off, the formatting is sloppy and that in itself can merit insta-downvotes. Please use the templates on the How to Write an SCP Guide to get proper bolded headers.
The containment is highly problematic because you have a lot of details that you don't really need. Why are the measurements "6 m x 8 m x 10 m" needed? 6 meters is about 19 feet, almost as high as a 2-story building. At that point, it's almost a small warehouse, not a chamber. Furthermore, if nothing terrible will happen if one of the dimensions is, say, 7 meters, there's no need to require specifics. Additionally, if you blank out information, how is anyone supposed to know what to do? The containment procedures are important instructions that everyone handling the object should be aware of. Also, who is Dr. ██████ and why are they the only person who can give permission? It's a security liability to have so much depend on just one person, who can easily be unavailable or indisposed. I say take that out entirely. There's a fair bit more, but it start, I recommend reading this guide on containment to get a feel for how to write more logical, resource-conserving procedures.
With regards to the concept… it's pretty bad. Right from the start:
SCP-4090 is a white humanoid figure of unknown origin. It appears to be 240 cm (7’9’’) tall and 60 kg (132 lbs), with no visible sensory organs. The upper body and appendages of SCP-4090 are shrouded with a grey gaseous substance (SCP-4090-1).
You don't need the non-metric measurements… the Foundation works only with metric. Furthermore, there's no need to note "unknown origin", and the use of the word "shrouded" is too flowery to come off as clinical. The rest of your description is ultimately just a bunch of details about its various powers and effects, more like a video game boss than a professional scientific report.
Remember that humanoids are actually among the most difficult types of articles to write successfully; if you're really set on writing one, then first take a look at the humanoid writing guide if you haven't yet.
I recommend getting the base idea polished up in the Ideas and Brainstorming forum before you try fixing the draft. Go to that forum, post a quick summary of the concept you want to write up (don't link the draft unless someone asks), and reviewers there can help you make the idea more interesting