@lyghtningwither The Yggdrasil thing is a matter of how fast your client makes requests to Mojang's authentication servers, if you don't see the exception then your client is probably just giving enough time between the requests that the server's don't complain.
From what I've read elsewhere the client should catch that exception and basically say "Oh ok, I'll wait a bit and try again"
If you want to make a Server-Side GUI I don't think you can use anything from Minecraft's built-in GUI Utilities, you will likely need to build one from scratch.
Edit: I am an idiot who did not read the whole thread
Two mods are trying to register the same metal with Tinkers, you'll have to choose which one to use or check the config for both mods to see if you can stop one of them from registering it.
If mods are programmed to identify themselves properly, mods that don't need to be on one of the sides with be automatically ignored by Forge, so it's good practice to have them all on both sides.
Unfortunately some mods stick with their own hosting, such as AnimalsPlus which I don't see on Curseforge. Mods like this can usually be found through links posted on the Minecraft Forum, but you should always be wary downloading mods regardless.
I know how to do it, I was testing how complete the effect would be and beyond vanity, i.e. the display name, there seem to be no other changes unless a password is also provided.
Please see http://stopmodreposts.org, 9Minecraft is known to rehost mods without permission, stick ads on mod downloads, and mark them as compatible with versions that they are NOT in order to get more clicks.