Warning: This riddle is designed for those who have a sizeable amount of experience in webriddles.

If this isn't your first riddle or you've just finished reading this then you can skip all of this.
If not then some quick rules.

Rules

Don't leak any answers.

Don't cheat.

Hints are allowed but solving this riddle (or any other, for that matter) is more fun when done with hints kept to a minimal.

Help

Answers go before the .htm in the level's URL to get to a new page.
This game uses a lot of ciphers to encrypt information. A good site to find the majority of them is dcode.fr.
An egg page is a new page that isn't a level, but rather a hint, an easter egg, etc. If in this riddle, there isn't an egg for something, it's either unrelated to the level, is easily inferrable or just wasn't added at the creator's own volition.
Even if you think a method you came up with won't work, you should still try it. In some levels (emphasis on the later ones) the solution might not make sense at first glance, or the solution might use/reference something relatively obscure.
Now that you've finished reading this, go back to the first line.