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when i try to start a minecraft forge mod (pixelmon) i says that the game does not support that modded version!! please help!!

---- Minecraft Crash Report -------- Minecraft Crash Report ----
WARNING: coremods are present:Contact their authors BEFORE contacting forge
// You're mean.
Time: 1/17/19 1:02 PMDescription: Initializing game
java.lang.VerifyError: Bad return typeException Details: Location: Config.getDefiningResourcePack(Lnet/minecraft/server/network/NetHandlerLoginServer;)Lnet/minecraft/profiler/Snooper; @91: areturn Reason: Type 'net/minecraft/util/CombatEntry' (current frame, stack[0]) is not assignable to 'net/minecraft/profiler/Snooper' (from method signature) Current Frame: bci: @91 flags: { } locals: { 'net/minecraft/server/network/NetHandlerLoginServer', 'net/minecraft/potion/PotionHealthBoost', 'java/util/Collection', 'java/util/List' } stack: { 'net/minecraft/util/CombatEntry' } Bytecode: 0x0000000: b202 cdb6 0388 4c2b b603 8e4d 2cc0 0335 0x0000010: 4e2d b903 3801 0004 6436 0415 049b 002e 0x0000020: 2d15 04b9 033c 0200 c003 a23a 0519 05b6 0x0000030: 03a5 3a06 1906 b203 7e2a b903 8103 0099 0x0000040: 0006 1906 b084 04ff a7ff d3b8 03a9 b203 0x0000050: 7e2a b603 d399 0007 b803 a9b0 01b0 Stackmap Table: full_frame(@27,{Object[#665],Object[#906],Object[#915],Object[#821],Integer},{}) same_frame(@69) chop_frame(@75,1) same_frame(@92)
at java.lang.Class.getDeclaredFields0(Native Method) at java.lang.Class.privateGetDeclaredFields(Class.java:2583) at java.lang.Class.getField0(Class.java:2975) at java.lang.Class.getField(Class.java:1701) at net.minecraftforge.fml.client.FMLClientHandler.detectOptifine(FMLClientHandler.java:293) at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:216) at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:467) at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:378) 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:497) at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

A detailed walkthrough of the error, its code path and all known details is as follows:---------------------------------------------------------------------------------------
-- Head --Thread: Client threadStacktrace: at java.lang.Class.getDeclaredFields0(Native Method) at java.lang.Class.privateGetDeclaredFields(Class.java:2583) at java.lang.Class.getField0(Class.java:2975) at java.lang.Class.getField(Class.java:1701) at net.minecraftforge.fml.client.FMLClientHandler.detectOptifine(FMLClientHandler.java:293) at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:216) at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:467)
-- Initialization --Details:Stacktrace: at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:378) 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:497) at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
-- System Details --Details: Minecraft Version: 1.12.2 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: 573938176 bytes (547 MB) / 1073741824 bytes (1024 MB) up to 3221225472 bytes (3072 MB) JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx3G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0 FML: Loaded coremods (and transformers): Launched Version: 1.12.2-forge1.12.2-14.23.5.2807 LWJGL: 2.9.4 OpenGL: GeForce GTX 1060 6GB/PCIe/SSE2 GL version 4.5.0 NVIDIA 368.81, NVIDIA Corporation GL Caps: Using GL 1.3 multitexturing.Using GL 1.3 texture combiners.Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.Shaders are available because OpenGL 2.1 is supported.VBOs are available because OpenGL 1.5 is supported.
Using VBOs: Yes Is Modded: Definitely; Client brand changed to 'fml,forge' Type: Client (map_client.txt) Resource Packs: Current Language: ~~ERROR~~ NullPointerException: null Profiler Position: N/A (disabled) CPU: 4x Intel(R) Core(TM) i5-3570K CPU @ 3.40GHz

That's not an error I'm familiar with but a place I would start is to make sure you are using the correct/updated version of Forge for the version of Minecraft and mods you are running and maybe also update Java.

how do i know if i use the correct? im newbie

You're using Minecraft 1.12.2, be sure the version of Forge you're using matches that version of Minecraft, it will say so on the Forge download page. Also be sure all your mods are compatible with that version as well, again, there will be links on the mod's download page that match what version of Minecraft they are for.