Undertale

- You can't avoid every fight, but you never have to escalate the violence.

- There is a way to spare everyone.

- There is only one exception to these rules, and you will know it when it happens.

- The Kill Everyone ending means kill everyone, not just everyone who gets in your way.

- You can't open the door with the mushrooms until after you've gotten the true pacifist ending.

- The Stick (your starting weapon) has multiple uses.

- Don't be ashamed of looking up the solution to the piano puzzle. It's optional, but also kind of poorly designed.