Flat models

[Friedslick6]

1. Take four rips of the model from all four side positions with the same animation frame and camera position. (You'll want a camera position as close to straight as possible to reduce perspective warping.)
   
2. Import the front and left side rips into a model editor.
   
3. Delete irrelevant tris from the scene.
   
4. Set the origin/pivot point of both models to their X/Z centre (X/Y in Blender), and then move them to the centre of the scene.
   
5. Position the front and left side in a model editor as an intersection using snap tools. (If you're in Blender, centre the cursor to 0,0,0 first.)
   
6. Scale the left side's bounding box to match the dimensions of the front side's.
   
7. Find a reference vertex visible from both sides and attempt to line them up for improved scaling accuracy.
   
8. Repeat steps 2-6 for the back and right side.

You can also perform this method with the front and back side, or the left and right side, for further improved scaling accuracy.

Thankfully Sonic the Fighters models do not use vertex colours, so missing tris should be easy to fill in and colour using the tris surrounding it.