I'd guess that this fight would be more difficult than most RAY jumping around everywhere from the stage to the background and back, firing a barrage of missiles towards the stage, and swiftly sweeping its tail. While REX is far more iconic, you fight RAY way more often. As for why I chose this over Shake King? Because Wario World needs more love.
I'd imagine the same would be translated into a Super Smash Bros. A simple fight however, as the Jewel only appears to fire lasers and slam itself into the ground to produce shockwaves.
SUPER SMASH BROS BRAWL BOSSES CRACK
It represents Wario's greed rather well, coming to have a crack at him. My choice, the Black Jewel from the ever bizarre Wario World.
SUPER SMASH BROS BRAWL BOSSES SERIES
Warioware isn't exactly a series with standard boss fights, which means I would need to search in the classic Wario games. I would imagine him breathing fire in various ways, jumping into the background and pouncing on the stage again, and charging forward? I guess Hewdraw could work, too if anything, just for mid-fight dialogue. While there are several bosses to choose from, I feel Twinbellows would fit a boss fight smoother than various other candidates. No idea how the fight would play out just wanted to fill in a Fire Emblem boss. The difference between this situation and Deathborn? I care far less about this than the latter, so I just chose the main antagonist from Ike's game line. Once again, I know very little about these 2. Maybe give him some more personality and/or a voice? All I remember of Deathborn is that he is a villain and at some point was holding Black Shadow up by the neck, so I guess make him into a sort of Ganondorf type boss? I'm too lazy to do research on him. The first fight where I have no idea in how it would go. Maybe add some new attacks and animations? A mega evolution would be cool for a phase 2 with Dragon Ascent and Draco Meteor. Simply port over the fight from Super Smash Bros. Hands would be the initial weak points, but once they are gone, Andross would resort to slamming his head into the stage, allowing for it to be attacked. We have his Super Nintendo form as an assist trophy already, so why not have one of his Nintendo 64 or higher forms as a boss? Attacks would consist mostly of hand swipes and projectile vomiting from the head in the background.
Fight would mostly be the same, gravity and all, but fighter attacks would be the source of damage rather than pegs jutting out from the platform's surface. Probably one the the most popular fights in the entire Yoshi franchise fighting on a small circular stage with its own gravity. The difference is Kraid would have more animations this time around, launching projectiles from his claws and abdomen maybe causing some rocks to fall from the ceiling? Would mostly be vulnerable when he leans in toward the stage. The stage would just be a similar layout to Brinstar Depths Kraid would come out of the depths below and strike the stage, causing it to spin. We finally got Ridley as a playable fighter, so may as well rely on his cohort to fill in the role of a boss battle. Attacks would simply be fireballs and rolling across the screen. Honestly, this fight would probably end up something like the Rathalos fight, only the item that drops would be an explosive of sorts, and the opportunity to use the item would be when King Dodongo opens his mouth. As for the phases of the fight, forget them. Fight would go similar to the one in his original game, but instead of tossing cannonballs, the fighter would just be jumping and attacking. Unfortunately for him, his hands served as platforms. Kerozene's attacks would consist of using Kleavers and breathing a nasty flame onto the field. Kerozene was probably one of the few good things about the Gameboy Advance port of Donkey Kong Country 2 a brand new boss that nobody had seen before the port was released. Now we actually touch on conceptualizing.
A reinstatement of the Brawl fight would be enough to bring back the first major fight in the Subspace Emissary. While he does have a presence in the game already, it is that of a Final Smash which pays homage to the boss fight in Super Smash Bros. Also, I have not played every series that is featured, so please understand if I chose one character(s) when another would have been a better fit. As such, the existing bosses in the game will receive no further explanations. Some of them are, or already have been bosses this is to sort of unify the concept with the results. I have chosen at least 1 from most of each series represented on the roster. This image contains various candidates of my choosing for potential boss fights that would have been interesting to see. Ultimate has a rather fine collection of bosses, but also missed opportunities for bosses that could've been fun to challenge.