So, Minecraft 1.12 crashes at startup, even though I'm pretty sure I did everything right
Here's the crash dump:
---- Minecraft Crash Report ----

WARNING: coremods are present:
LoadingPlugin (Quark-r1.2-97.jar)
Contact their authors BEFORE contacting forge

// Ouch. That hurt :(

Time: 6/28/17 2:09 AM
Description: There was a severe problem during mod loading that has caused the game to fail

net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Quark (quark)
Caused by: java.lang.NoClassDefFoundError: vazkii/quark/vanity/recipe/ElytraDyingRecipe
at vazkii.quark.vanity.feature.DyableElytra.preInit(DyableElytra.java:47)
at vazkii.quark.base.module.Module.lambda$preInit$1(Module.java:128)
at vazkii.quark.base.module.Module$$Lambda$72/1011923463.accept(Unknown Source)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at vazkii.quark.base.module.Module.forEachEnabled(Module.java:187)
at vazkii.quark.base.module.Module.preInit(Module.java:128)
at vazkii.quark.base.module.ModuleLoader.lambda$preInit$2(ModuleLoader.java:80)
at vazkii.quark.base.module.ModuleLoader$$Lambda$71/972564142.accept(Unknown Source)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at vazkii.quark.base.module.ModuleLoader.forEachEnabled(ModuleLoader.java:158)
at vazkii.quark.base.module.ModuleLoader.preInit(ModuleLoader.java:80)
at vazkii.quark.base.proxy.CommonProxy.preInit(CommonProxy.java:31)
at vazkii.quark.base.proxy.ClientProxy.preInit(ClientProxy.java:39)
at vazkii.quark.base.Quark.preInit(Quark.java:35)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:647)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:252)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:230)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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:147)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:615)
at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:267)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:466)
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)
Caused by: java.lang.ClassNotFoundException: vazkii.quark.vanity.recipe.ElytraDyingRecipe
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 55 more
Caused by: java.lang.NoClassDefFoundError: vazkii/arl/recipe/ModRecipe
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
... 57 more
Caused by: java.lang.ClassNotFoundException: vazkii.arl.recipe.ModRecipe
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:101)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 61 more

I have a similar problem, but I am using Forge (Twitch app), so the class that is accused to be missing is not the Dyable Elytra, but RedBlock (ReedBlock.preInit(ReedBlock.java:41)).

`---- Minecraft Crash Report ----

WARNING: coremods are present:
LoadingPlugin (Quark-r1.2-97.jar)
Contact their authors BEFORE contacting forge

// Would you like a cupcake?

Time: 6/28/17 11:38 AM
Description: There was a severe problem during mod loading that has caused the game to fail

net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Quark (quark)
Caused by: java.lang.NoClassDefFoundError: net/minecraftforge/fml/common/registry/IForgeRegistryEntry
at vazkii.quark.building.feature.ReedBlock.preInit(ReedBlock.java:41)
at vazkii.quark.base.module.Module.lambda$preInit$1(Module.java:128)
at vazkii.quark.base.module.Module$$Lambda$72/1927390025.accept(Unknown Source)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at vazkii.quark.base.module.Module.forEachEnabled(Module.java:187)
at vazkii.quark.base.module.Module.preInit(Module.java:128)
at vazkii.quark.base.module.ModuleLoader.lambda$preInit$2(ModuleLoader.java:80)
at vazkii.quark.base.module.ModuleLoader$$Lambda$71/1189829644.accept(Unknown Source)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at vazkii.quark.base.module.ModuleLoader.forEachEnabled(ModuleLoader.java:158)
at vazkii.quark.base.module.ModuleLoader.preInit(ModuleLoader.java:80)
at vazkii.quark.base.proxy.CommonProxy.preInit(CommonProxy.java:31)
at vazkii.quark.base.proxy.ClientProxy.preInit(ClientProxy.java:39)
at vazkii.quark.base.Quark.preInit(Quark.java:35)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:647)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:252)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:230)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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:147)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:615)
at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:267)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:466)
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)
Caused by: java.lang.ClassNotFoundException: net.minecraftforge.fml.common.registry.IForgeRegistryEntry
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 55 more
Caused by: java.lang.NullPointerException
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
... 57 more

A detailed walkthrough of the error, its code path and all known details is as follows:

-- System Details --
Details:
Minecraft Version: 1.12
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 784355056 bytes (748 MB) / 973602816 bytes (928 MB) up to 3817865216 bytes (3641 MB)
JVM Flags: 4 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx4096m -Xms256m -XX:PermSize=256m
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.40 Powered by Forge 14.21.0.2379 6 mods loaded, 6 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UCH minecraft{1.12} [Minecraft] (minecraft.jar)
UCH mcp{9.19} [Minecraft Coder Pack] (minecraft.jar)
UCH FML{8.0.99.99} [Forge Mod Loader] (forge-1.12-14.21.0.2379.jar)
UCH forge{14.21.0.2379} [Minecraft Forge] (forge-1.12-14.21.0.2379.jar)
UCE quark{r1.2-97} [Quark] (Quark-r1.2-97.jar)
UCE autoreglib{1.2-8} [AutoRegLib] (AutoRegLib-1.2-8.jar)
Loaded coremods (and transformers):
LoadingPlugin (Quark-r1.2-97.jar)
vazkii.quark.base.asm.ClassTransformer
GL info: ' Vendor: 'Intel' Version: '4.3.0 - Build 10.18.14.4578' Renderer: 'Intel(R) HD Graphics 4400'`

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