Shredder's Changes?

[Drose18]

Can anyone explain how shredder went from super tall hairless, scarred to a way shorter guy with a beard and man bun?

[Mew]

Shredder knew that with the new helmet he has, he can now wear a fabulous man-bun. He had wanted this hairstyle all his life, but his original suit wouldn't allow it! With his new hairdo, the Shredder can defeat the turtles knowing he doesn't have to have a reflective, shiny head that distracts from his equally shiny armor.

That's my theory.

[The Deadman]

He was wearing platform shoes.

[Candy Kappa]

(And there is nop way that mutagen got through the armor and healed him! that's fan headcannon!)

the inner lining of his glove isn't armor, though.

http://orig06.deviantart.net/78f6/f/2016/151/f/6/shredderoozyhand_by_candykappa-da4hdtw.jpg

[Candy Kappa]

Shredder regenerating from a scarred 80+ year old man to a hunky Brian Tee after having foreshadowing-splooge covering his fingers is one of the lesser issues with the movie(s), and have some in-canon explanation.

There's a huge ass snow-covered mountain right next to New York City, though... Unless Sacks so rich he can dump enough rocks to make his very own ski resort.