As you also see in the top row of the crash log, you see "Couldn't get hash for net/minecraftforge/forge/1.12.2-14.23.1.2555/forge-1.12.2-14.23.1.2555.jar from files.minecraftforge.net/maven/net/minecraftforge/forge/1.12.2-14.23.1.2555/forge-1.12.2-14.23.1.2555.jar.sha1: HTTP 404: Not Found"

Which can also be that you tried some mod that is not capable to run in 1.12.2.
Same problem happend to a person trieng to download shaders for his 1.12.2 minecraft, but he got the 1.7.2 version on his 1.12.2. Which doesnt work at all. It will crash.
Some mods from older patches, will not work with the new ones, some do and some dont.
If this is not the case, you should re-download everything and make sure they are applicable to your version.
Also, if you have 32 bit java on a 64 bit computer, you will automaticly run on a lower ram setting, this causes crashes too. Make sure that is correct.

I also see you have this one "main WARN Unable to instantiate org.fusesource.jansi.WindowsAnsiOutputStream""

you could try:
1. install the Microsoft Visual C++ 2008 Redistributable Package, OR
2. add -nojline after -jar bukkit.jar in your run.bat

get the Visual C++ 2008 Redistributable:

for 32 bit: http://www.microsoft.com/en-gb/download/details.aspx?id=29
for 64 bit: http://www.microsoft.com/en-gb/download/details.aspx?id=15336

If none of these works for you. Let me know and I'll try to figure it out for you.

Also make sure if you are installing seperate mods and putting them into your own folder, you should follow their install instructions (If they have one), as some mods needs to have their "mods" away from the "core" part.