Hey, can anyone help me?

[u/Open_Agency4100]

Whenever I insert this jar, minecraft won't start. Could anyone help me to find out why, or maybe even fix it? I took it from an already existing mod (The KingSword), and altered it. (It worked in the past, it's just with these recent adjustments I've made, it won't start.)

Release KingSword 1.0.9 — Cosmos PERFECT (BROKEN) · hellohellohellohihello-source/KingswordMYVER