Lucas Sullivan: Kaptain K. Rool (Donkey Kong Country 2)
I would go with the Giant Baby from Zombies Ate My Neighbors, but he’s more “precocious-toddler-turned-giant-mutant” than a true boss fight. That’s why I’ve settled on the hefty crocodile pirate who first kidnapped Donkey Kong. K. Rool was amazing for the sheer amount of stuff he shot at you, each with its own unclear but present danger. He’s probably one of the most grueling-but-fair bosses I ever encountered as a kid.
K. Rool’s primary attack was a barrage of spiked cannonb--excuse me, kannonballs shot from his oversized blunderbuss. These were easy to dodge at first--but the death-balls would fly with increasingly wonky patterns, eventually whirling at you in slo-mo loop-de-loops that wreak havoc on your jump timings. When he wasn’t blasting kannons your way, K. Rool fired colored clouds (which looked vaguely like trapped monkey souls) that could freeze you, slow you, or reverse your controls. Oh yeah, and he would intermittently turn invisible AND teleport around trying to hit you. You also have to fight him twice to see the true ending, and his Krocodile Kore incarnation is exponentially more difficult. What a baller.