I'll reference Nintendo IPs, even if the games are not Nintendo made.
In terms of being a ripoff from another game - Gohdan from Wind Waker wins this category.
Whoever from Nintendo designed this boss was so lasy that they just took Andross from Star Fox and reskinned it and put it in a Zelda game. If that's not what happened, it sure as hell feels like it. Most lazy design of any Zelda boss ever.
In terms of being hard? Hmmmmm.
Culex from Mario RPG is actually quite hard.
Andross from Star Fox Zero is also very hard and also not very fun at all.
Prime on hard mode from Metroid Prime really takes skill to beat.
Dark Samus at the end of Metroid Prime 2 need skilla and luck to beat.
K.Rool inside the volcano in Donkey Kong Country 3 is hard but not super hard. With some practiceit's doable.
K.Rool from Donkey Kong 64 needs perfect timing to beat. One screw up and the round resets which makes the entire battle impossible it beat. it's doable, just really hard. Also really annoying to lose right at the end and have to re-do all the other rounds over and over.
Shadow from Zelda 2 is very hard if you don't cheese the AI.
Majora's Mask from the same game has some challenge to it if you don't use the Fierce Deity Mask.
It's not the worst 3D Zelda game ever made. Well worth a play. It's not amazing, but it's also not garbage either.
if you’re gonna say gohdan you might as well lump in bongo bongo, the boss in the desert level of Mario 64, sigma from mega man x, and a few others. singling out gohdan specifically is a little unfair.
I know, I’m specifically surprised that Spirit is recommending SS. I too think it’s a good game, far better than TP anyway.