Minecraft Mod troubles?

Today I decided to download some fish mods as I was building an aquarium. But every time I join my world it shuts down the Internal Server and says this

The game crashed whilst unexpected error
Error: java.lang.IndexOutOfBoundsException: 18496

It won't let me click on the crash report either, I've tried 3 different mods and I still get this message! I think it's the forge but i'm not sure (This forge was working a few months ago)

Why won't my Minecraft load? - 1

Ever since I got forge minecraft won't load. I have deleted forge and all mods. I have deleted minecraft and then re-download it. It still won't load. It gets stuck on the MOJANG screen.

Mods for Minecraft on Macbook pro?

I'm trying to download Mods for minecraft on my little sister mac.

Can someone please give me an in depth step by step? All the one I've found online are outdated.

My sisters computer is a macbook pro, and I just tried to download the most recent update of forge.

I can't open the Java Jar file because I keep getting the error message that says;

"forge- 1. 12. 1- 14.22. 1. 2485-universal.jar" could not be launched. Check the Console for possible error messages."

Can anyone help me trouble shoot this?

Minecraft launcher won't start

I double clicked on the Minecraft shortcut and the Minecraft icon appears on the taskbar below but the launcher is not coming up. I try clicking on it but that doesn't work. I tried to delete all the files of Minecraft and downloaded again but it doesn't work. I also tried to do the repair thing where you download it while you still have it but no results. Also, the problem might lye in the fact that in the .minecraft folder the only thing there's the launcher data. There's no mods folder or server file or worlds folder or anything.

Lost my worlds on Minecraft?

I was getting some mods, and after playing a bit my worlds were gone from the other snapshots? I don't know what to do.