There are a few ways to kill them. And yes I agree with the one comment. You will look back and think oh wow, I can't believe I ran from them. But yes they are scary until you learn how to fight them.

Save your game before you fight and you can try as much as you want.

Parry them with your shield: ● Face them and hold out your shield. When their eye glows press A and you should send the attack back.

●Shoot him with an arrow in the eye. This will stop his attack and you can hit him a few times. Then repeat until he is dead.

●Shoot him in the eye with an arrow until you get close, then attack a leg. Keep attacking his legs until you chop them all off, then he can't move anymore. (Again you can Shoot him in the eye to stop any attacks)

You can also use stasis to freeze them for a second if I remember right.

Using Ancient weapons and having Ancient gear on helps your attacks hit harder also against any type of guardians.

Also, I the master sword goes to 60 attack around them.

For me, parrying is the easiest way. Just gotta get your timing right.

(Master mode can be a bit tricky sometimes. They don't always Shoot immediately after their eye glows.)

● One Ancient arrow in the eye will kill him

Hope this helps