I have the 1.8.9 version (To play hypixel with it) and I have Optifne_1.8.9_HD_U_M5 installed. This mod, when paired with optifine, causes minecraft to crash on startup.

1.8.9 is unsupported. Why do you need uteamcore for that version?
If you are using the musicplayer mod you can remove uteamcore for the 1.8.9 version

I am sorry, I just relised I put this in the wrong area, sorry