Learn Hardcore Russian: Пускай первый дротик оказался промахом, ты не промахнёшься снова. - Even if the first dart was a miss, you will not miss again.

Breakdown of Пускай первый дротик оказался промахом, ты не промахнёшься снова.

What does пускай mean here? Is it literally let?

Not really. Here пускай is being used in a concessive sense, meaning something like:

So Пускай первый дротик оказался промахом means something like Even if the first dart was a miss or Granted that the first dart missed.

Russian пускай can also mean let in commands, but that is not the main sense here.

Is пускай the same as пусть?

Yes, they are very close. In many sentences they can be swapped:

Both can mean let or even if / granted that, depending on context.

The difference is mostly stylistic:

So this sentence could also be written as:

Why is there a comma after промахом?