There is no official "Shadow in Sonic 3 & Knuckles" game or ROM.
Shadow the Hedgehog did not exist until Sonic Adventure 2 (2001), years after Sonic 3 & Knuckles (1994). Any ROM claiming to feature Shadow in S3&K is a fan-made hack/romhack, not an official Sega release.
The persistent search for this non-existent game speaks to a larger fan desire: What if Shadow were a classic character? Shadow In Sonic 3 And Knuckles Rom Download
A few legendary modders have injected Shadow into the classic 16-bit masterpiece. The most famous ones include: There is no official "Shadow in Sonic 3
Moreover, Shadow's origin story in SA2 involves Project Shadow and Gerald Robotnik. Because Sonic 3 & Knuckles features Angel Island, the Master Emerald, and hidden laboratories (like Hidden Palace), fans have retroactively tried to connect Shadow’s creation to the floating island. Part 5: Why the Obsession with Shadow in the Classic Era
The Elusive Shadow: Uncovering the Truth Behind Shadow in Sonic 3 and Knuckles ROM Download
. The most common ways to experience this are through standalone Genesis ROM hacks or the modernized Sonic 3 A.I.R. Popular Shadow ROM Hacks & Mods Sonic 3 & Knuckles: Episode Shadow