The ROM hack Sonic 3: D.A. Garden Edition, first released in 2015, comes to Sonic 3 A.I.R.! This mod, with approval from and made in correspondence with the original hack creator, brings plenty of new content to both the A.I.R. and D.A. Garden Edition experience:

• From Angel Island Zone to The Doomsday Zone, enjoy a full game's worth of new level layouts and special stages adjusted for A.I.R.'s widescreen ratio and feature set.
• New times of day and weather give old settings a fresh feel. Aesthetic changes can be disabled via the Options menu if desired.
• Level layouts from the original ROM hack have been adjusted to maintain flow and reintroduce zone gimmicks.
• Knuckles' campaign contains a more difficult game! More than one Eggrobo is out to keep Knuckles at bay, and a new set of Blue Spheres special stages will test your mind and reflexes. Difficulty changes can be disabled via the Options menu if desired.
• Enter the Challenges menu to prove your speed supremacy in two distinct modes! Find the fastest paths in a straightforward Time Attack mode, or tackle Time Stone Trial mode and collect timer-stopping Mini Time Stones without losing your rings. Credit to AirWay1 for his Custom Menu Framework.
• Looking to submit to speedrun.com? Activate Marathon mode from the Options menu to remove many cutscenes and level transitions from the Normal Game mode, or activate the No Emeralds Marathon mode to remove giant rings as well. Credit to ElspethThePict for her Custom Text Display mod. These modes must be played via Normal Game or Act Select; A.I.R.'s dedicated Time Attack mode does not support script mods.
• Play a dedicated Green Sphere game mode to prove your special stage supremacy. Credit to Fred Bronze for his original take on green spheres.

To use:

• Open Sonic 3 A.I.R. (v22.08.27.0 or later required; v22.09.10.0 suggested)
• Right-click in the game window and choose to open the mods folder.
• Place the ZIP file (unzipping not needed!) into the mods folder.
• Close and re-open Sonic 3 A.I.R. to have the game scan for the mod.
• After the Sonic 3 A.I.R. title screen, enter the MODS menu, select Sonic 3: D.A. Garden Edition, and hold A+Left to shift the mod from the Inactive column to the Active column.
• Return to the A.I.R. main menu and select NORMAL GAME to access the D.A. Garden Edition main menu.