Okay. I have your measurements. You might need to add another 0.1-0.5 if you are wanting a little slack/looseness, or making double pouches
Originals (96-97, Originals, Angels, Devils, Santas, Mothra,Ocean, Caveman and MCD toys of 97)
Originals SIZES= 2.2in x 2in
Tamagotchi Mini SIZES= 1.1in x 1.1in
Versions 1,2 connections SIZES= 2.1in x 2in
Version 3 connection SIZES= 2.3in x 2in
Version 4 connection SIZES= 2.6in x 2in
Version 4.5 connection SIZES= 2.7 x 2in
Version 5, 5.5 connections SIZES= 3in x 2in
Version 6 connection SIZES= 2.1in x 2in
Version 7 SIZES 2.8in x 2.0 x 2.0 (The extra 2.0 is the thickness)
Best dementions for Originals are 2.5in x 2.5in
Best dementions for Tamagotchi Mini is 1.5in x 1.5in
Best dementions for Versions 1-3,6 are 3in x 3in
Best dementions for Versions 4- 5.5 are 3.4in x 3in
Best dementions for 7/Tama-go are 4in x 4in
If you are sewing on the inside and turning the case inside out, add a few more partical inches based on how close you sew to the edge. If you sew 0.5 inches in from the edge, I would recommend adding 0.5 inches to the best dementions I've given to you. Otherwise, the tamagotchi will be a bit more stung inside the pouch you are trying to create.
Hope this helps you!