In this run of Sonic 3 & Knuckles, Sonic has decided that getting all the emeralds is the only way to go and as such powers his way through the special stages to achieve this (and a perfect ending). This run also avoids using a glitch called horizontal underflow, which is explained in the author's comments.
The downloadable encodes in the second set use a camhack, which attempts to always keep Sonic onscreen and puts HD sprites on top of the background to make the TAS look even better.
We also have similar movies with Sonic and Tails, Amy, Knuckles, Tails, Knuckles ring attack, Knuckles 100%, Competition mode and Sonic and Tails on NewGame+.
FLASHING LIGHTS WARNING: 37:15 onwards, Hyper Sonic will have moments of a bright flash that some users may find to be discomforting