My friend has had issues with a modpack that i made, he joined my server when i recently installed the Morph mod. while he was jumping around with a slime sling he suddenly crashed.

From then onwards he crashed when he joined any world or server. I have told him to remove all mods and keep it bare bones with just forge installed and it loaded successfully.

This was the error message after he redownloaded the mods i gave:

---- Minecraft Crash Report ----

WARNING: coremods are present:
  ForgelinPlugin (Forgelin-1.8.4.jar)
Contact their authors BEFORE contacting forge

// Surprise! Haha. Well, this is awkward.

Time: 5/19/23 1:11 PM
Description: Updating screen events

java.lang.NullPointerException: Updating screen events
    at com.gildedgames.the_aether.client.gui.trivia.AetherTrivia.getNewTrivia(AetherTrivia.java:33)
    at com.gildedgames.the_aether.client.gui.AetherLoadingScreen.func_73721_b(AetherLoadingScreen.java:43)
    at net.minecraft.client.Minecraft.func_71353_a(Minecraft.java:2474)
    at net.minecraft.client.Minecraft.func_71403_a(Minecraft.java:2430)
    at net.minecraft.client.Minecraft.func_71371_a(Minecraft.java:2344)
    at net.minecraft.client.gui.GuiCreateWorld.func_146284_a(GuiCreateWorld.java:224)
    at net.minecraft.client.gui.GuiScreen.func_73864_a(GuiScreen.java:443)
    at net.minecraft.client.gui.GuiCreateWorld.func_73864_a(GuiCreateWorld.java:416)
    at net.minecraft.client.gui.GuiScreen.func_146274_d(GuiScreen.java:533)
    at net.minecraft.client.gui.GuiScreen.func_146269_k(GuiScreen.java:501)
    at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1759)
    at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1098)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:398)
    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 thread
Stacktrace:
    at com.gildedgames.the_aether.client.gui.trivia.AetherTrivia.getNewTrivia(AetherTrivia.java:33)
    at com.gildedgames.the_aether.client.gui.AetherLoadingScreen.func_73721_b(AetherLoadingScreen.java:43)
    at net.minecraft.client.Minecraft.func_71353_a(Minecraft.java:2474)
    at net.minecraft.client.Minecraft.func_71403_a(Minecraft.java:2430)
    at net.minecraft.client.Minecraft.func_71371_a(Minecraft.java:2344)
    at net.minecraft.client.gui.GuiCreateWorld.func_146284_a(GuiCreateWorld.java:224)
    at net.minecraft.client.gui.GuiScreen.func_73864_a(GuiScreen.java:443)
    at net.minecraft.client.gui.GuiCreateWorld.func_73864_a(GuiCreateWorld.java:416)
    at net.minecraft.client.gui.GuiScreen.func_146274_d(GuiScreen.java:533)
    at net.minecraft.client.gui.GuiScreen.func_146269_k(GuiScreen.java:501)

-- Affected screen --
Details:
    Screen name: net.minecraft.client.gui.GuiMainMenu
Stacktrace:
    at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1759)
    at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1098)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:398)
    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: 480037416 bytes (457 MB) / 1442840576 bytes (1376 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: 0, tallocated: 0
    FML: MCP 9.42 Powered by Forge 14.23.5.2859 21 mods loaded, 21 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                                |
    |:------ |:--------------- |:----------------- |:--------------------------------------------- |:---------------------------------------- |
    | LCHIJA | minecraft       | 1.12.2            | minecraft.jar                                 | None                                     |
    | LCHIJA | mcp             | 9.42              | minecraft.jar                                 | None                                     |
    | LCHIJA | FML             | 8.0.99.99         | forge-1.12.2-14.23.5.2859.jar                 | e3c3d50c7c986df74c645c0ac54639741c90a557 |
    | LCHIJA | forge           | 14.23.5.2859      | forge-1.12.2-14.23.5.2859.jar                 | e3c3d50c7c986df74c645c0ac54639741c90a557 |
    | LCHIJA | aether_legacy   | 1.5.3.2           | aether-1.12.2-v1.5.3.2.jar                    | None                                     |
    | LCHIJA | betternether    | 0.1.8.6           | betternether-0.1.8.6.jar                      | None                                     |
    | LCHIJA | byg             | 1.7.1             | BiomesYouGo1.7.1.jar                          | None                                     |
    | LCHIJA | codechickenlib  | 3.2.3.358         | CodeChickenLib-1.12.2-3.2.3.358-universal.jar | f1850c39b2516232a2108a7bd84d1cb5df93b261 |
    | LCHIJA | mantle          | 1.12-1.3.3.55     | Mantle-1.12-1.3.3.55.jar                      | None                                     |
    | LCHIJA | jei             | 4.16.1.1000       | jei_1.12.2-4.16.1.1000.jar                    | None                                     |
    | LCHIJA | tconstruct      | 1.12.2-2.13.0.183 | TConstruct-1.12.2-2.13.0.183.jar              | None                                     |
    | LCHIJA | conarm          | 1.2.5.10          | conarm-1.12.2-1.2.5.10.jar                    | b33d2c8df492beff56d1bbbc92da49b8ab7345a1 |
    | LCHIJA | customspawner   | 3.11.4            | CustomMobSpawner-3.11.5.jar                   | None                                     |
    | LCHIJA | mocreatures     | 12.0.5            | DrZharks-MoCreatures-Mod-12.0.5.jar           | None                                     |
    | LCHIJA | enderstorage    | 2.4.6.137         | EnderStorage-1.12.2-2.4.6.137-universal.jar   | f1850c39b2516232a2108a7bd84d1cb5df93b261 |
    | LCHIJA | forgelin        | 1.8.4             | Forgelin-1.8.4.jar                            | None                                     |
    | LCHIJA | exnihilocreatio | 1.12.2-0.4.7.2    | exnihilocreatio-1.12.2-0.4.7.2.jar            | None                                     |
    | LCHIJA | waila           | 1.8.26            | Hwyla-1.8.26-B41_1.12.2.jar                   | None                                     |
    | LCHIJA | journeymap      | 1.12.2-5.7.1      | journeymap-1.12.2-5.7.1.jar                   | None                                     |
    | LCHIJA | naturescompass  | 1.8.5             | NaturesCompass-1.12.2-1.8.5.jar               | None                                     |
    | LCHIJA | tinkersjei      | 1.2               | tinkersjei-1.2.jar                            | None                                     |

    Loaded coremods (and transformers): 
ForgelinPlugin (Forgelin-1.8.4.jar)
  
    GL info: ' Vendor: 'NVIDIA Corporation' Version: '4.6.0 NVIDIA 531.79' Renderer: 'NVIDIA GeForce GTX 1050 Ti/PCIe/SSE2'
    Pulsar/tconstruct loaded Pulses: 
        - TinkerCommons (Enabled/Forced)
        - TinkerWorld (Enabled/Not Forced)
        - TinkerTools (Enabled/Not Forced)
        - TinkerHarvestTools (Enabled/Forced)
        - TinkerMeleeWeapons (Enabled/Forced)
        - TinkerRangedWeapons (Enabled/Forced)
        - TinkerModifiers (Enabled/Forced)
        - TinkerSmeltery (Enabled/Not Forced)
        - TinkerGadgets (Enabled/Not Forced)
        - TinkerOredict (Enabled/Forced)
        - TinkerIntegration (Enabled/Forced)
        - TinkerFluids (Enabled/Forced)
        - TinkerMaterials (Enabled/Forced)
        - TinkerModelRegister (Enabled/Forced)
        - wailaIntegration (Enabled/Not Forced)

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Please update to a modern version of Minecraft to receive support.

Currently supported versions are 1.19.4 (Latest) and 1.18.2 (LTS).