Why he not allowed to have mechanical pencils or any pen/cils more than 8 millimetres wide?
He may shove pens and pencils into his ear.
Mechanical pencils come with those thin graphite rods that he can put into his ears.
What's with the lead poisoning in 2006?
In December 2005, a paper was published detailing findings of high levels of lead in Beethoven's hair. All in all it supported the theory that Beethoven was afflicted with lead poisoning. It should be obvious what SCP-3817 did next.
Are you trying to degrade Mendelssohn? Why do you hate him so much? What's the significance of all this?
Nope. Not at all. Mendelssohn is, in fact, my favorite composer. I'm really fond of him. His Violin Concerto in E minor is amazing. Also. The Hebrides overture. Piano Concerto no. 1. Midsummer Night's Dream. And of course the Songs Without Words mentioned in the article. The list goes on.
This SCP was written mainly as a critique to the popular view that Mendelssohn wrote music that was light and superficial because of him living in relative comfort in comparison to other composers. Mendelssohn is commonly described as being someone who did not suffer in his life and was always happy.
And that is not true.
Mendelssohn did suffer a lot in his lifetime. While he wasn't sickly, nor poor, nor severely mentally ill, he did have quite the capricious temperament. Additionally, he suffered from depression from time to time, and frequently doubted the quality of his own work. Finally, he was ridiculously overworked, especially in the last decade of his life. I don't think anyone would consider being overworked not suffering.
And Mendelssohn was not superficial, in any sense of the word. Stylistically speaking, he was generally conservative and not as bombastic as his peers, but this was due to his musical education - in his early years, he was exposed to the music of Bach, Mozart, Beethoven etc, so they became his stylistic role models. Mendelssohn's music was not "revolutionary" in any way, but that does not make his works shallow and superficial.
Also, the SCP in general is meant to critique the idea that suffering naturally leads to good art (or results of elevated quality in general). While enduring hardships is a way people can become stronger, overdosing on suffering for the sake of suffering is more likely to result in detrimental effects than beneficial ones.