

Sure, the Heavy King is actually capable of harming Super Sonic, costing you 10 rings each time, but during the entire final battle, an unlimited number of rings spawn and drift around the arena, and they're attracted to you as if you have a Lightning Shield, note if you use Debug Mode to place a Special Stage ring and head inside, the pre-boss cutscene plays again when you leave the Special Stage, which reveals that Sonic actually does receive a Lightning Shield once he transforms and the fight begins proper so it's not a big problem if you manage to dodge his attacks, and the invincibility frames are often easy to exploit to get a free hit.


Alternatively, if you're able to get a Lightning Shield or Super Mode and keep them before entering this particular boss, his electric shock phase becomes a complete joke, as you're immune to it. As you break off his chains by damaging him, it becomes easier to get an optimal position, since his shock will have a smaller area of affect. Even though the final boss can typically be tedious and challenging due to its multiple phases, it becomes surprisingly easy and brief if you get the hang of positioning yourself right above Robotnik without excess horizontal momentum whenever his electric shock phase begins, and landing as many hits as possible on Robotnik during his downtime.
