Calculus 2

Calculus decided that it got tired of being scrawny, so it started injecting steroids and hitting the gym... then, it became Calculus 2.

Widely considered the hardest conventional math class at the university level, to pass this class, you need to be determined and willing to cry yourself to sleep every night because of how agonizing it is.

Keep in mind, Calculus 3 is Calculus 2 after forgetting to take PCP when it finished its steroid cycle.