Whenever I load a New World with the Mod Installed it Crashes the game, What do I do?
(Crash Report Below)

---- Minecraft Crash Report ----
// There are four lights!

Time: 6/7/20 8:50 PM
Description: Exception in server tick loop

java.lang.NoSuchMethodError: net.minecraftforge.fml.relauncher.ReflectionHelper.getPrivateValue(Ljava/lang/Class;Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object;
at com.crowsofwar.avatar.common.util.AvatarUtils.(AvatarUtils.java:61)
at com.crowsofwar.avatar.common.data.BendingData.writeToNbt(BendingData.java:511)
at com.crowsofwar.avatar.common.data.AvatarPlayerData.writePlayerDataToNBT(AvatarPlayerData.java:81)
at com.crowsofwar.gorecore.data.PlayerData.writeToNBT(PlayerData.java:128)
at com.crowsofwar.gorecore.data.PlayerData$1.writeV(PlayerData.java:61)
at com.crowsofwar.gorecore.data.PlayerData$1.writeV(PlayerData.java:33)
at com.crowsofwar.gorecore.util.GoreCoreNBTUtil.writeMapToNBT(GoreCoreNBTUtil.java:161)
at com.crowsofwar.gorecore.data.WorldDataPlayers.func_189551_b(WorldDataPlayers.java:55)
at com.crowsofwar.avatar.common.data.AvatarWorldData.func_189551_b(AvatarWorldData.java:88)
at net.minecraft.world.storage.MapStorage.func_75747_a(SourceFile:92)
at net.minecraft.world.storage.MapStorage.func_75744_a(SourceFile:78)
at net.minecraft.world.WorldServer.func_73042_a(WorldServer.java:1053)
at net.minecraft.world.WorldServer.func_73044_a(WorldServer.java:1001)
at net.minecraft.server.MinecraftServer.func_71267_a(MinecraftServer.java:407)
at net.minecraft.server.integrated.IntegratedServer.func_71267_a(IntegratedServer.java:252)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:170)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:523)
at java.lang.Thread.run(Thread.java:745)

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 10 (amd64) version 10.0
Java Version: 1.8.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 314028280 bytes (299 MB) / 738197504 bytes (704 MB) up to 2147483648 bytes (2048 MB)
JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
IntCache: cache: 0, tcache: 8, allocated: 20, tallocated: 86
FML: MCP 9.40 Powered by Forge 14.21.1.2387 7 mods loaded, 7 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UCHIJAAAA minecraft{1.12} [Minecraft] (minecraft.jar)
UCHIJAAAA mcp{9.19} [Minecraft Coder Pack] (minecraft.jar)
UCHIJAAAA FML{8.0.99.99} [Forge Mod Loader] (forge-1.12-14.21.1.2387.jar)
UCHIJAAAA forge{14.21.1.2387} [Minecraft Forge] (forge-1.12-14.21.1.2387.jar)
UCHIJAAAA mercurius_updater{1.0} [mercurius_updater] (MercuriusUpdater-1.12.jar)
UCHIJAAAA gorecore{1.12.2-0.4.5} [GoreCore] (avatarmod-1.5.17-alpha.jar)
UCHIJAAAA avatarmod{1.5.17-alpha} [Avatar Mod: Out of the Iceberg] (avatarmod-1.5.17-alpha.jar)
Loaded coremods (and transformers):
GL info: ERROR RuntimeException: No OpenGL context found in the current thread.
Profiler Position: N/A (disabled)
Player Count: 1 / 8; [EntityPlayerMP['Stonebend'/674, l='New World', x=155.50, y=70.00, z=242.50]]
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fml,forge'

I think you need to update your forge.

You are using an outdated MinecraftForge version. As noted basically everywhere where you can get this mod, it needs the latest MinecraftForge version to run.