How can I defeat guardians?

Solution 1:

This Reddit post has the same question, and leads to two videos (of the demo) of players defeating guardians: a moving one, and an immobile one.

• Moving guardian : the player turns around the guardian, dodging its attacks, and firing explosive arrows to weaken it. Then he fires an arrow directly to its eye, which destroys it.
• Immobile guardian : the player fires arrows to the guardian eye while it is preparing an attack. Then, between each guardian fire, the player hits it with his sword, until the guardian is defeated. The player will eventually dodge the guardian's attacks, as they are one-shot-attacks.

Also, it has been proven that any shield can parry a guardian laser attack back at it to defeat it. This is the quickest method, though you need good timing. Immobile guardians only require one parried attack, but mobile guardians require that you parry 3 attacks back at them.

Ancient arrows will also make short work of guardians, purchasable at the Akkala Ancient Tech Lab.

As stated in the comments by @Dabbingsdednow, you can use all three charges of Urbosa's Fury (also known as the Power of Urbosa or Urbosa'a Power) to defeat a guardian.

Solution 2:

Guardian Stalkers' legs are vulnerable to attack. And so are the propellers of the airborne ones according the to loading screen tip.

My preferred method is to shoot the eye to stun it, then attack & destroy a leg. Keep stunning it and going after the other 5 legs to do quite a bit of damage. By the time it is legless, you can finish it off easily. Be sure to grab the parts the destroyed legs drop!