Honestly, this is a really creative idea for Audino. I like the whole "still kind, but tough as nails now" idea you got going for it. I can actually see it working perfectly in Pokémon Desolation, with all those cities and their districts.
I do have some design suggestions about it if you're still wanting some creative feedback on it:
- For its main (common) sprite, give it a whole new color scheme. Grey could work very well, like you said. But if this A-Audino design is specifically made from the preferences of Martin, maybe you could also give it a brown or yellow color scheme? As for its shiny sprite, I think the original Audino color scheme could work nicely as a reference, with pink clothes or boots.
- This is a little detail suggestion, but maybe you could give it a little tool to hold? Like a mallet or power drill? Random side note, I think an Audino holding a little mallet in battle would look pretty adorable lol.
- If you're planning to also give it a Mega Evolution, I think I have a suggestion: muscles. BIG muscles. Well, probably not muscles too big, but just enough to notice. You know how the original Mega Audino has an innocent, cute, and overall mystical look to it? How about giving A-Audino's Mega Evolution a rougher look? Kinda like a combination between it and Gurdurr. I just think giving it a sterner and more intimidating look would really set the appealing difference between the two variations.
But yeah, those are my slight design suggestions for A-Audino. Hope they will be of some use for you!