The Hardest (and only) Quiz in OSC is a quiz about the OSC.
It says "Count V!". The answers are "AH!", "How cute!" and "Erm… one?". The correct answer is "Erm… one?", due to it saying count V.
It says "?bmud tibbaRehTyeulB si ". The choices are "Erm… what?", "seY" and "oN". The answer is "seY".
The objective is to click the bottle with lemonade, but there are four, all being wrong. To proceed, click the phrase "bottle with lemonade".
You need to move your cursor to the red dot. The maze will come up, but it's impossible to cross normally. To get past, move your cursor outside the quiz and go back in the quiz screen, this time on the other part. Click the other dot to proceed.
It gives you a clue that the answer is really big, but they all seem big. One is a big variant of the word "answer", just the phrase "really big", a cropped frame of the golden infinity from Heist and just the phrase "an elephant". The answer is "an elephant".
The objective is to search for Leafy, but she's surrounded by lots of Fireys. There are 13 Fireys. Click on Leafy to proceed.
It asks for the correct answer location for Question 2. Even though it was in the bottom left box, the correct one is the top right.
It instructs you to choose a drink, but there are only 4 Bloods, labeled "Blood". The third one from the left surprisingly doesn't take a life away. Click that Blood 45 times to peel off the label, revealing another label, this time saying "Tomato Juice". Click on said Blood once more to proceed.