Invincibility frames (i-frames)

Invincibility frames are the moments during an action when hits pass straight through the player. Most games put them at the start of a dodge roll or a dash, so a well-timed dodge through an attack works and a badly timed one doesn't.

How long should i-frames last?

Long enough to cover the movement and a little beyond it, so a dodge timed right never gets clipped on its last frame. Short enough, and limited enough, that pressing dodge over and over isn't a safe way to play.

I-frames in Mytheria

The first 0.2 seconds of every dash are a dodge, slightly longer than the dash itself, which lasts 0.16 seconds. While the window is open the character shimmers a cool blue, so you can see when you're safe. The first five times a dash carries you through a hit in a world, a small "Dodged" appears over you; after that it stops, because by then you know.

What keeps the dash from being an escape button is charges. You start with one, and it comes back 0.76 seconds after you use it. A dodge only means something if you can see the attack coming, which is why every enemy attack in Mytheria is telegraphed.