I installed tough as nails latest version for 1.12.2, with nothing else, and launched it with forge for 1.12.2 and it crashes.
I tried installing glitchcore, but that didn't change anything.

Here is the portion of the crash log that seems to include the error:

[17:31:20] [main/FATAL] [FML]: The following problems were captured during this phase
[17:31:20] [main/ERROR] [FML]: Caught exception from toughasnails (Tough As Nails)
java.lang.NullPointerException: null
at toughasnails.init.ModConfig.lambda$init$0(ModConfig.java:64) ~[ModConfig.class:?]
at toughasnails.init.ModConfig$$Lambda$138/2102583800.apply(Unknown Source) ~[?:?]
at toughasnails.init.ModConfig.populateDataMap(ModConfig.java:92) ~[ModConfig.class:?]
at toughasnails.init.ModConfig.init(ModConfig.java:64) ~[ModConfig.class:?]
at toughasnails.core.ToughAsNails.init(ToughAsNails.java:73) ~[ToughAsNails.class:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:600) ~[forge-1.12.2-14.23.3.2668.jar:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76) ~[guava-21.0.jar:?]
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116) ~[guava-21.0.jar:?]
at com.google.common.eventbus.EventBus.post(EventBus.java:217) ~[guava-21.0.jar:?]
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:280) ~[LoadController.class:?]
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:258) [LoadController.class:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76) ~[guava-21.0.jar:?]
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71) ~[guava-21.0.jar:?]
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116) ~[guava-21.0.jar:?]
at com.google.common.eventbus.EventBus.post(EventBus.java:217) ~[guava-21.0.jar:?]
at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:149) [LoadController.class:?]
at net.minecraftforge.fml.common.Loader.initializeMods(Loader.java:755) [Loader.class:?]
at net.minecraftforge.fml.client.FMLClientHandler.finishMinecraftLoading(FMLClientHandler.java:352) [FMLClientHandler.class:?]
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:534) [bib.class:?]
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:377) [bib.class:?]
at net.minecraft.client.main.Main.main(SourceFile:123) [Main.class:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
[17:31:20] [main/INFO] [STDOUT]: [net.minecraft.init.Bootstrap:func_179870_a:553]: ---- Minecraft Crash Report ----

Time: 4/19/18 5:31 PM
Description: There was a severe problem during mod loading that has caused the game to fail
net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Tough As Nails (toughasnails)
Caused by: java.lang.NullPointerException
at toughasnails.init.ModConfig.lambda$init$0(ModConfig.java:64)
at toughasnails.init.ModConfig$$Lambda$138/2102583800.apply(Unknown Source)
at toughasnails.init.ModConfig.populateDataMap(ModConfig.java:92)
at toughasnails.init.ModConfig.init(ModConfig.java:64)
at toughasnails.core.ToughAsNails.init(ToughAsNails.java:73)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:600)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:280)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:258)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:149)
at net.minecraftforge.fml.common.Loader.initializeMods(Loader.java:755)
at net.minecraftforge.fml.client.FMLClientHandler.finishMinecraftLoading(FMLClientHandler.java:352)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:534)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:377)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

I get exactly this same crash whenever I try to add any items to the block_temperature.json

I get the same crash, I think it's linked to new Forge versions. :(

It seems to be some weird fringe case with mod loading order. I've had it happen a few times when launching from eclipse in my dev environment, but it didn't do it when I relaunched it after.

I haven't any ideas what cause this crash, it happens without any other mods. I think it's the new forge versions which mess with TAN.

I got the same crash when only using the mod tough as nails, deleted the config folder and regenerated it. Works fine now

I can't reproduce this with a fresh instance.

https://i.imgur.com/MFvDYJM.png
and
https://paste.ee/p/iZ0XI

Have you tried deleting your config files for the mod?
I had a similar problem, until I tried deleting the config.

Any updates regarding this?