The reason it may be hard to jot this idea down in the SCP style may be an unfamiliarity with the detached clinical tone used in SCP articles, which can be a pain to really master without absorbing some of the writing here, excluding SCPs in the "first" series (002-999), as the older SCPs aren't really written to today's standards. In the guide hub, located in the top bar, you can find a guide on clinical tone that goes into further detail about how to describe things in am appropriate manner.
As for the idea, its coming across as completely random. Why a deer antler? Why does it have these effects? How does an invincible monster play into the idea? The elements come across as disparate and unconnected, and without any further information and connective tissue, it just seems like a few ideas that sound cool until they're put to paper.
Beyond that, it is recycling elements that are seen quite often around here: evil monsters that can't be killed, items that cause degenerative mental effects are both overdone things. It might be useful to take some time to read more recent works to see what's successful nowadays, as co cepts like this have been being thrown at the site for a decade now, and need some original twist or unique detail to make them stand out.
Best of luck.
