I just downloaded pixelmon for 1.10.2 and I try to load it and it just crashes, Here's the crash log
 

---- Minecraft Crash Report ----
// Would you like a cupcake?

Time: 1/7/18 5:11 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 Pixelmon (pixelmon)
Caused by: java.lang.IllegalAccessError: tried to access field net.minecraft.client.renderer.entity.RenderManager.field_178636_l from class com.pixelmonmod.pixelmon.client.ClientProxy
    at com.pixelmonmod.pixelmon.client.ClientProxy.registerRenderers(ClientProxy.java:238)
    at com.pixelmonmod.pixelmon.Pixelmon.init(Pixelmon.java:114)
    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.EventSubscriber.handleEvent(EventSubscriber.java:74)
    at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
    at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
    at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
    at com.google.common.eventbus.EventBus.post(EventBus.java:275)
    at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:243)
    at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:221)
    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.EventSubscriber.handleEvent(EventSubscriber.java:74)
    at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
    at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
    at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
    at com.google.common.eventbus.EventBus.post(EventBus.java:275)
    at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:145)
    at net.minecraftforge.fml.common.Loader.initializeMods(Loader.java:795)
    at net.minecraftforge.fml.client.FMLClientHandler.finishMinecraftLoading(FMLClientHandler.java:324)
    at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:520)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:351)
    at net.minecraft.client.main.Main.main(SourceFile:124)
    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)

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

-- System Details --
Details:
    Minecraft Version: 1.10.2
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_25, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 617987528 bytes (589 MB) / 2164260864 bytes (2064 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=16M
    IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
    FML: MCP 9.32 Powered by Forge 12.18.3.2185 5 mods loaded, 5 mods active
    States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
    UCHI    mcp{9.19} [Minecraft Coder Pack] (minecraft.jar)
    UCHI    FML{8.0.99.99} [Forge Mod Loader] (forge-1.10.2-12.18.3.2185.jar)
    UCHI    Forge{12.18.3.2185} [Minecraft Forge] (forge-1.10.2-12.18.3.2185.jar)
    UCHI    mercurius_updater{1.0} [mercurius_updater] (MercuriusUpdater-1.10.2.jar)
    UCHE    pixelmon{1.2.1} [Pixelmon] (PixelmonGenerations-1.2.1.jar.zip)
    Loaded coremods (and transformers):
    GL info: ' Vendor: 'NVIDIA Corporation' Version: '4.6.0 NVIDIA 387.92' Renderer: 'GeForce GTX 1050/PCIe/SSE2'

This is an issue with Pixelmon. Make sure you're using the latest version and report it to the author.

Pixelmon is no longer in development, and has been officially taken down due to a C&D by the Pokemon Company. It has not been possible to download Pixelmon for almost a year now, so any download that you have is both illegal and unofficial.

 

Link to shutdown thread: http://pixelmonmod.com/viewtopic.php?f=5&t=25183