You fight Gekko as a mini-boss twice, and I absolutely love Gekko. I honestly kind of debated putting the Dinolfos in the 'regular enemies' segment, because as the game goes on multiple Dinolfosi keeps showing up as mini-bosses in different parts of the game. The Dinolfos breathes fire, and fire means instant-death for your poor Deku Scrub form.
In Majora's Mask, however, a Dinolfos (alternatively Dinolfols in the original translation) is the first mini-boss you fight, and the Dinolfos is particularly deadly at the stage of the game you meet him in. The Dinolfos have a minor role in Ocarina of Time, only showing up in the Gerudo Training Grounds.
A very, very fun little battle, even if design-wise the Ikana characters are just ultimately fantasy skeleton people. There's a fun bit of vampire-esque goodness to the fight, where Link has to permanently 'destroy' Igos and his bodyguards' bodies by dealing the finishing blow on the parts of the throne room where the sunlight shines down. Igos himeslf fights like a regular Stalfos, but he does have a bunch of wacky attacks befitting a boss fight, including a poison gas breath, and his head will split off from his body and fly around at one point. Igos himself looks real fancy with that ornate cape, sword and shield (particularly in the artwork and the MM3D remaster) It's a simple thing, and they could've simply made Igos's two bodyguards regular Stalfoses without changing much, but I liked that they went the extra route. The two bodyguards basically are reskinned versions of the Stalfos from Ocarina of Time, although I do like that they added the simple addition of making them take on the trope of 'one skinny guy, one fat guy'. You fight King Igos du Ikana and his two unique-model bodyguards in the former throne room of the Ikana Kingdom, all of whom have been brought back to life because of the emergence of the Stone Tower.
Pretty fun, and the fact that Keeta is a giant is always something that the game never explains. In practice, he's basically a giant Stalchild with two tiny hands on top of his head, and Link basically has to re-enact Skull Keeta's final battle in order to get him to properly 'rest', allowing him to properly pass on his 'duty' to Link. I'm not going to spoil the entire story but Skull Keeta is basically the gigantic captain of the now-undead Ikana forces. Majora's Mask is kind of interesting in that each area (the swamp, the snow mountains, the great bay and the canyon) all have their own stories and storylines that you have to complete before tackling each respective dungeon, and for the fourth segment, the Ikana Canyon, some of the fights involve you fighting against, well, bosses. We'll start off with the 'overworld bosses'. We covered the normal monsters before, now we're going to cover the overworld bosses, minibosses and dungeon bosses! but it sure really feels like such a more complete experience. And you don't have to play Ocarina to play Majora's Mask. To the uninitiated, Majora's Mask works off of the same N64 engine that Ocarina of Time ran on, so the developers were able to re-utilize a lot of the combat mechanics and general assets from that game, allowing them to focus more on designing the story and how everything else fits together in the game.
but it's still basically my favourite in terms of the trippy world-building, the gameplay mechanics, the storyline, and the very dream-like vibe of whatever is going on. I'm not here to talk about the gameplay or the story or the vibe of the game as a whole. Its graphics is sure outdated now, and even the 3DS remake doesn't really bring it up to current HD standards or whatever, but I really do still love this game. I don't think it's an exaggeration for me to say that the Legend of Zelda: Majora's Mask is a strong contender for my favourite Legend of Zelda game of all time.