I defeated Garl Vinland in Demon's Souls Remake with my bow-only character by parrying his swings and firing arrows while he was stunned. Here's the video. Below, I'll share insight into my approach.
Every time I replay a Souls game, I like to attempt feats of skill I haven't tried before. It keeps the game interesting to me, someone who--like many of you!--has beaten it more times than he can count. One way I spice up each playthrough of Demon's Souls is to kill the boss of world 1-4 early. He's traditionally the (real) final boss, so I'll kill him early and choose the boss of another boss as my final challenge.
I ran a bow-only build in the OG Demon's Souls, and Maiden Astraea was the biggest challenge. Not because of Astraea herself, but because of her protector, Garl Vinland. Garl's deal is to plant himself in the narrow path leading to Astraea and block. He's a turtler, and the only way to make him come out of his shell is to get close enough to bait him into attacking. In the PS3 version, I defeated Garl Vinland by parrying his attacks and using the time he was stunned to roll into him. Every roll nudges him slightly, so the idea was to nudge him out of my way and reach Astraea, then kill her before he could race over and squash me flat with his giant hammer.
This time, I wanted to think bigger. Grander. Tougher. What if, I wondered, I could parry Garl Vinland's hammer swings, and then draw my bow and fire before he could raise his shield? It would be complex, and the timing would be crucial, but I'd done something like this before. In a recent playthrough of the Dark Souls remaster on PS4, I ran a bow-only character and killed the rightmost silver knight archer in Anor Londo using the same technique. The first time I attempted it, I parried successfully. Yay, right? Go me?
Well, I was so surprised my plan was working that I stood there gaping like an idiot long enough for the silver knight to recover and smack me with his sword. I proceeded to parry and fire an arrow twice more without taking a hit. But Garl Vinland is a lot stronger than that silver knight. He has a deep pool of hit points, and, again, his giant hammer is gigantic. The gigantic giant hammer. So, I set another personal challenge: I would defeat Garl by parrying and firing--and I would not allow myself to take a single hit. If I took damage, I would save and quit, which loads your character outside the boss's fog gate and resets their HP. It took several tries, but it worked.
Then Garl Vinland threw a curveball: When his HP was nearly depleted, he blocked my arrows, something he hadn't done up to that point. How did I adapt? I won't spoil it. Just watch.