He’s shining on you…
Light that reflects off a prism produces the color of the rainbow.

Duckie’s saying that he’s freestyling easily like arithmetic which is the basic form of math and he sounds good doing it.

He’s saying he doesn’t need prescription medicine for his sickness because the weed will make him feel better.

Doctors give prescriptions to sick people.

Regardless of how abnormal Shad Fer is,he’s still a great rapper.
Also clever play on words considering combining the words mutant and unusual=mutual.

Due to rappers like Kendrick,J.Cole,Big K.R.I.T,A$AP Rocky e.t.c making it big,people are starting to think that real rap will soon takeover the radio and Shad feels the same way, considering he wants to be one of those rappers.

He was careful about the way he planned out his take over and he wants to prove that his young age won’t matter in the end.

By stealing the game in the explanation above,his sick and devious plan is successful because he beat the mainstream rappers by trusting his skill and not selling out.As a result of this,the mainstream rappers will be mad because his lyricism and rapping abilities makes their ‘hard’ raps look basic and mediocre.

He’s stealing the rap game from the popular mainstream rappers that claim it.

Shad’s describing his slow growth in popularity by comparing his flow to the way a king cobra slithers,slowly,but smoothly,like water lol.He calls it a King Kong cobra because an actual cobra’s size is pathetic compared to Shad’s raps.