This mod is for the 2004 PC version of Sonic Adventure DX. You will need to install the SADX Mod Loader to use it: https://info.sonicretro.org/SADX_Mod_Loader . If you have the Steam version, you can convert it with PkR's SADX Mod Installer: https://www.moddb.com/mods/sadx-dreamcast-conversion/news/new-mod-installer-now-available1
SA2 Sonic is a mod that ports Sonic's model from SA2(B) into SADX. This was made possible by, of all things, the Cream the Rabbit cameos added to the DX version of the game, which use the same model format as SA2's character models. I (MainMemory) implemented custom code to override Sonic's regular rendering function and instead load and render the original model and animation data from SA2B. This also affects Metal Sonic and Super Sonic, who have their respective models and animations from SA2 as well. For animations that exist in SADX but not in SA2 (eg showering), End User converted them to work with SA2's model structure. In addition to this, the mod's configuration options (accessed by highlighting the mod in the mod manager and clicking the "Configure..." button) have options to replace Sonic with Shadow or Amy, as well as several alternative costumes for all characters, including the Dreamcast models, Sonic's Trial model, and Amy and Rouge's outifts. Additionally I have ported the jiggle effect on Sonic/Shadow/Amy's spines directly from SA2.
At this time, picking up objects does not work properly, and a couple animations that were converted from SADX for the SA2 models are a bit broken.
The source code for this mod is available at https://github.com/MainMemory/SADXChunkModels