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)
When you mean you can't click on the crash report, do you mean a message comes up and you can't click it? If so then you should have a crash report file in your Minecraft folder, would you be able to find that and copy-paste it to https://pastebin.com and give me the link?
Without the crash report, the best advice I could give you is copy your world/save file and delete everything and start again, copy back your save file and see if that works.
As a note, you should double check that the new mods you installed are the correct version for your version of forge.
No