||GET A LOAD OF THIS!
— Dr. Robotnik
The Egg Viper is the fifth and final boss of Sonic's story in Sonic Adventure. After being led through Lost World by Tikal, and shown an incomprehensible vision of slaughtered chao outside a burning Emerald Shrine, Sonic returned to the surface of Mystic Ruins just in time to spot the Eggmobile en route to Eggman's groundside base. The blue hedgehog follows, pitting him against the game's longest level, Final Egg. In a massive vertical shaft at the core of the base, Sonic confronts his old nemesis, piloting this armoured, mechanical serpent.
Amongst the Viper's various attacks are him strafing the platforms with lasers, launching crackling balls of blue plasma, hurling spinning spiked disks, and wrecking up Sonic's footholds themselves. The boss can most easily be damaged when it extends its tail to charge the blue plasma attack. Flashing green nodes form a homing attack chain that leads right to Robotnik, who pops out of his cockpit apparently to do a mocking dance at Sonic, leaving him open for hurt.
Even when the health bar is whittled down to nothing, Sonic still isn't safe. Indeed, the final attack is the most dangerous, as the flailing and thrashing of the defeated Viper sees it smash through yet more platforms, and requires extremely quick homing attacks or spin dashing to get out of the way. But once evaded, Sonic's story is clear.