>>724918274
Due to the way the game handles collision data with the spikes, using the level 4 sword (the Golden Sword) makes Mothula immune to almost every attack you can do with it. The only attacks you can do are sword beams and the little poke when holding a spin attack. This also applies to doing spin attacks with the level 3 sword (the tempered sword), and if you hit Mothula with the fire rod while it's over spikes, you won't do any damage to it
>just use the fire rod anyway
That's what it's for, yep. But if the Golden Sword did function properly, you would do more damage with it during this fight than the Fire Rod could ever do. The GBA version fixes this oversight and you can beat Mothula in 3 hits with the Golden Sword if you wanna postpone this dungeon until then.