When you're about half-healthy, he'll admit you have some power, but summon a might holy hammer and Elden Ring Runes swing it in a arc front of him in order to gain momentum, allowing it to fly into the air, then slam down upon you. Take a backswing from the initial swing, and wait until he's close to falling to stay out of the direction of the hammer. Then defend yourself - but be prepared for the next dagger strikes.
Additionally, he can summon a stronger golden sword blade, which has greater reach than his daggers, and can use it in conjunction with his cane to create slash combos that are hard to avoid, or end by slashing with his main staff weapon.
Margit can be a challenge to determine which magical weapon they'll summon and how they'll integrate them into his combo attacks. Therefore, you'll need stamina ready to block or dodge his next move. If you've got a good absorbent shield, you could even perform Guard Counters at the same time, but make sure that he's completed his combo attack prior to initiating your counter. Otherwise, you'll be more vulnerable once you're fully committed to the attack.
Make sure to take your time during this battle and be patient, as he moves slow enough for you to have time to watch his animations and impression of the correct and wrong time to practice your own techniques - and don't get greedy enough that you're left open. Melee fighters should back off at intervals to recuperate their full stamina. Then wait until he makes the first move so you can react accordingly.Get your hits where you are able to Cheap Elden Ring Items gradually cut Margit down. He'll drop with enough time clearing the path to Stormveil Castle proper.