When the fight against Yhorm first starts, run straight for the throne at the very end of the room. At the foot of throne, you’ll find the Storm Ruler sword (!), which is vital for winning this fight, unless you want to spend hours dealing 60 damage to Yhorm’s feet.
After you’ve grabbed the sword, either equip it, or use a Homeward Bone to get out of the arena so you can spend some time getting used to the sword’s move set. We suggest putting your shield away for this fight. Yhorm’s attacks are very heavy and can deplete your stamina even with a decent shield for blocking. Thankfully, even though he hits hard, it’s very easy to dodge his attacks. He has an overhead swing where he smashes his blade into the ground right in front of him, and you can evade this simply by rolling between his legs.
He has a slightly more dangerous sweep attack where he swings his blade in a wide arc in front of him. This can hit you if you’re standing at his side, but you can also use your i-frames to dodge this fairly easily. Occasionally, Yhorm will stomp his foot on the ground, creating a shockwave that pushes you back. This won’t deal any damage to you, but you will have to take a few seconds to recover and get back up on your feet.