DaemonUmbra

Where are you getting your mods?

How much ram do you have in your machine? I don't think this is directly related, but it's a frequent problem.

You should run genEclipseRuns.

What mods do you have installed?

Can you provide your debug.log? More info in my signature below.

Please read the "Logs" section of my signature below and provide the appropriate log in the appropriate manner.

How long have you waited before forcing the game to close?

Do not refer to dependencies as core-mods, the term coremod has a special meaning when it comes to Forge. I believe since you're using 1.12.2 you shouldn't need to do anything beyond putting your dependency jar in the libs folder and re-running setupDecompWorkspace

Have you tried the most recent version of Forge?

Please provide a screenshot of where the file is and of your command prompt with the command history showing.

User was banned for using a cracked launcher.

If your game is making fml-client-latest.log then first of all you should update to a version of Forge that isn't ancient (unless you're using a pre-made modpack).

What do you mean by core-mod... do you mean a dependency or do you mean a mod that directly modifies Minecraft code?

This is on Windows but as far as I know the important commands are common to both

Launch it from the command line(or in your case Terminal) and tell us what it says.

I'm assuming this is on the Twitch launcher? If so then there's nothing we can do here.

Installing isn't enough, you need to tell your computer which version to use, usually this is accomplished by using the full path to the java executable instead of just using "java" as a command

https://adoptopenjdk.net

You must use Java 8 when using Forge for 1.12.2 and earlier

I hate this video, the guy routes the description links through his won site for extra ad revenue.

User was banned for using a cracked launcher.

https://www.whatismyip.com

I don't know what version of Minecraft you're trying to make mods for but ForgeGradle 1.2 seems to indicate that i's ANCIENT.

Where are you getting your mods?

Check mods/1.12.2 , OTG likes to stick a jar in there that doesn't self-disable when you remove the main mod jar.