Complex sentence: Gobber had lost a hand, foot and tooth in battle with dragons over his lifetime, and he then replaced them with prosthetics built in his smithy; he also replaced Hiccup's left lower leg after Hiccup lost it in the original film.
Split into simpler sentences: Gobber had lost a hand, foot and tooth in battle with dragons over his lifetime, and he then replaced them with prosthetics built in his smithy. He also replaced Hiccup's left lower leg after Hiccup lost it in the original film.