If you want to beat Thunderblight Ganon in Zelda Breath of the Wild, you must use a one-handed weapon and a shield. The best weapon to use would be a sword such as the Guardian Sword or Master Sword. Having one of these swords or something similar alongside a shield is recommended. In short, having a decent one-hand weapon and shield will allow you to block the boss's attacks and deal decent damage during both phases of the fight. That said, here's how to beat Thunderblight Ganon during both stages of its Boss fight.
How to beat Thunderblight Ganon in the first phase in Zelda Breath of the Wild
To beat Thunderblight Ganon in the first part of its boss fight, you must use your one-handed weapon to deal a steady flow of damage to the boss. While attacking the boss, watch out for orb attacks that they will occasionally shoot toward your way. You can easily dodge these by walking out of the way. Keep attacking the boss after, and they will eventually make a fast rush attack. You will want to pull your shield out and deflect the attack when this happens. If you block the attack, you will stun Thunderblight Ganon and can deal heavy damage to him. Attacking Thunderblight Ganon while stunned should be enough to get his health bar down to half. When Thunderblight Ganon's health bar reaches half full, the second phase of the boss fight will start.
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How to beat Thunderblight Ganon in the second phase in Zelda Breath of the Wild
When Thunderblight Ganon starts the second phase of the fight, we recommend heading to the high ground on a nearby platform. This is because, during the second phase, Ganon will start dropping stone pillars on the ground, which deal heavy damage. Thunderblight Ganon will also be mid-air while he is dropping the pillars. To get Thunderblight back down to the ground, you will want to use the Magnesis ability to pick a pillar up and drop it on him. Doing so will make Ganon fall back to the ground where you can finish him off with fury strikes.
For more on Zelda Breath of the Wild and other Zelda games, we at PGG recommend checking out both How old is Link in BOTW and other Zelda games? and Is The Legend of Zelda: Twilight Princess coming to Nintendo Switch?