Chrono Trigger

Please note that this guide is riddled with spoilers, particularly in the endings section, and the walkthrough does describe the events on that chapter.

Walkthrough
Chapters are named and numbered according to the name of the saved game file during that point of the game. Since the ending essentially depends upon during what portion of the game Lavos is challenged a small section in each chapter will mention what will happen if you beat Lavos during that chapter.

While the walkthrough is mostly designed around a new game where you will be getting all of the equipment for the first time, Chrono Trigger also has the option to start a New Game + after you beat Lavos through the black omen. You'll be able to take all the levels of your characters and the contents of your save file (with a few exceptions such as the masamune and the bike key) and be able to start the game over with powered-up characters. In a New Game + it's also possible to challenge Lavos at almost any point by using the right telepad at the millenial fair. The game is considerably easier in a New Game +, making most of the challenge about completeness and finding all the endings.