My problem with the Death Egg Robot (both the Sonic the Hedgehog 2 version, its Sonic Generations iteration, or the contraption of the same name in Sonic Forces) is that you can't actually see Eggman in there. In spite of my love for Sonic Heroes, the Egg Emperor has the same issue. Same goes for the Kyodai Egg Robo from Sonic & Knuckles (yes, it's a different machine from the one in StH2), the final boss of Sonic Advance 2 (I don't know what that is named), the Egg King from Sonic Rush, and the Egg Wizard from Sonic Rush Adventure (though it's possible that the only reason we don't see Eggman in there is the graphical limitations of the original DS). If we're going to have a boss fight with Eggman in Smash, I’d rather have him using a machine where we can see him doing stuff like operating the controls, yelling taunts and insults at his opponent (bonus points if he has special lines for fighting Sonic), boasting about how powerful and dangerous his machine is while he's attacking, panicking a bit when his opponent gets close, expressing frustration and rage when he gets hit, laughing and gloating when he scores a hit, et cetera. Some of his contraptions that I feel would be suitable for a boss battle include the Big Arm from Sonic the Hedgehog 3, the Psyco Egg from Sonic CD (yes, the misspelling is intentional), the Egg Viper from Sonic Adventure, the Egg Dealer from Shadow the Hedgehog, the Egg Wyvern from Sonic the Hedgehog 2006, the Egg Dragoon from Sonic Unleashed (though it is admittedly tough to see Eggman operating it), and the Nega-Wisp Armor from Sonic Colors.