Modpack version
1.69

Issue
Instantly crashes after opening a Wireless crafting terminal, caused by the wither skeleton in the UI with the "Happy Halloween" writing underneath it, the crash log supports this too
Edit: I temporarily solved this by setting my laptops date to 10.30.2019 instead of 10.31.2019
Logs
https://pastebin.com/DymKzDZb

Thanks for the help md5i! Changing your PC date should resolve this issue :)

Confirmed here as well in 1.70:

java.lang.ClassCastException: net.minecraft.entity.monster.EntityWitherSkeleton cannot be cast to net.minecraft.entity.player.EntityPlayer
	at p455w0rd.wct.client.gui.GuiWCT.func_146273_a(GuiWCT.java:289)

This appears to have been reported here: p455w0rd/WirelessCraftingTerminal#356