when i try to start a new world its brings me to the lancher and it says
The game crashed whilst ticking entity
Error: java.lang.NoClassDefFoundError: com/pg85/otg/forge/dimensions/WorldProviderOTG
and the crash report
---- Minecraft Crash Report ----

WARNING: coremods are present:
OTGCorePlugin (OTG-Core.jar)
Contact their authors BEFORE contacting forge

// You're mean.

Time: 2/27/19 6:53 PM
Description: Ticking entity

java.lang.NoClassDefFoundError: com/pg85/otg/forge/dimensions/WorldProviderOTG
at com.pg85.otg.forge.asm.OTGHooks.getGravityFactorFallingBlock(OTGHooks.java:72)
at net.minecraft.entity.item.EntityFallingBlock.func_70071_h_(EntityFallingBlock.java:130)
at net.minecraft.world.World.func_72866_a(World.java:1993)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:832)
at net.minecraft.world.World.func_72870_g(World.java:1955)
at net.minecraft.world.World.func_72939_s(World.java:1759)
at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:613)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:767)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:185)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassNotFoundException: com.pg85.otg.forge.dimensions.WorldProviderOTG
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)
... 12 more
Caused by: java.lang.NullPointerException

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

-- Head --
Thread: Server thread
Stacktrace:
at com.pg85.otg.forge.asm.OTGHooks.getGravityFactorFallingBlock(OTGHooks.java:72)
at net.minecraft.entity.item.EntityFallingBlock.func_70071_h_(EntityFallingBlock.java:130)
at net.minecraft.world.World.func_72866_a(World.java:1993)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:832)
at net.minecraft.world.World.func_72870_g(World.java:1955)

-- Entity being ticked --
Details:
Entity Type: minecraft:falling_block (net.minecraft.entity.item.EntityFallingBlock)
Entity ID: 13
Entity Name: Falling Block
Entity's Exact location: -43.50, 7.01, -718.50
Entity's Block location: World: (-44,7,-719), Chunk: (at 4,0,1 in -3,-45; contains blocks -48,0,-720 to -33,255,-705), Region: (-1,-2; contains chunks -32,-64 to -1,-33, blocks -512,0,-1024 to -1,255,-513)
Entity's Momentum: 0.00, 0.00, 0.00
Entity's Passengers: []
Entity's Vehicle: ERROR NullPointerException: null
Immitating block ID: 13
Immitating block data: 0
Stacktrace:
at net.minecraft.world.World.func_72939_s(World.java:1759)
at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:613)

-- Affected level --
Details:
Level name: New World
All players: 0 total; []
Chunk stats: ServerChunkCache: 625 Drop: 0
Level seed: 5350062043047421108
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options:
Level spawn location: World: (112,64,-562), Chunk: (at 0,4,14 in 7,-36; contains blocks 112,0,-576 to 127,255,-561), Region: (0,-2; contains chunks 0,-64 to 31,-33, blocks 0,0,-1024 to 511,255,-513)
Level time: 4 game time, 4 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 112036 (now: false), thunder time: 94152 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: true
Stacktrace:
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:767)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:185)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:745)

-- System Details --
Details:
Minecraft Version: 1.12.2
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 816193176 bytes (778 MB) / 1140850688 bytes (1088 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: 0, allocated: 12, tallocated: 94
FML: MCP 9.42 Powered by Forge 14.23.5.2768 8 mods loaded, 8 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored

| State     | ID        | Version      | Source                               | Signature                                |
|:--------- |:--------- |:------------ |:------------------------------------ |:---------------------------------------- |
| UCHIJAAAA | minecraft | 1.12.2       | minecraft.jar                        | None                                     |
| UCHIJAAAA | mcp       | 9.42         | minecraft.jar                        | None                                     |
| UCHIJAAAA | FML       | 8.0.99.99    | forge-1.12.2-14.23.5.2768.jar        | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UCHIJAAAA | forge     | 14.23.5.2768 | forge-1.12.2-14.23.5.2768.jar        | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UCHIJAAAA | otgcore   | 1.12.2 - v7  | minecraft.jar                        | None                                     |
| UCHIJAAAA | cfm       | 6.2.0        | cfm-6.2.0-mc1.12.2 (2).jar           | None                                     |
| UCHIJAAAA | radixcore | 1.12.x-2.2.1 | RadixCore-1.12.x-2.2.1-universal.jar | None                                     |
| UCHIJAAAA | mca       | 1.12.2-5.3.1 | MCA-1.12.x-5.3.1-universal (2).jar   | None                                     |

Loaded coremods (and transformers): 

OTGCorePlugin (OTG-Core.jar)
com.pg85.otg.forge.asm.OTGClassTransformer
GL info: ERROR RuntimeException: No OpenGL context found in the current thread.
Profiler Position: N/A (disabled)
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fml,forge'

if some1 can help me then please help

I'm experience the same exact error after uninstalling/deleting all OTG dependent mods. upon closer inspection of my mod folder i found in its contents a folder called 1.12 which contained a OTG core mod separate from the main OTG Jar itself.

Upon deleting this 1.12 folder from within my mods folder in my profile manually that issue was solved.
Since not many folks manually install their mods anymore this sort of thing was bound to happen, but this is why i like using the manual method, i can get down and see what i'm dealing with within my folders directly instead of letting a twitch launcher handle it all. lol

You should see if this folder is within your installed mods still, and if so, delete that item, it should fix the issue entirely' if your not using any actual OTG dependent mods

Hey, thanks for reporting and thanks for helping @WilliamBlaze. Will see if we can improve this.

For v8_r3, I've added OTG-Core as a dependency with a specific version, so if an incorrect version of OTG-Core is used, OTG will not load on app start and the logs will contain a warning about OTG-Core version xxx missing. Unfortunately I can't rename OTG-Core.jar to include a version number, since having multiple OTG-Core.jars after updating would cause even worse problems. Users will have to understand that they should delete OTG-Core and restart MC to re-generate it, hopefully that won't cause (as many) problems... All I can do for now though. Thanks for the feedback!