Hack Unity Console GUI

ConsoleHijacker.cs

using System;
using System.Reflection;
using UnityEditor;
using UnityEngine;

public class ConsoleHijacker
{
    static readonly Type editorWindowDelegate = typeof(EditorWindow).Assembly.GetType("UnityEditor.HostView+EditorWindowDelegate");
    static readonly Font monospaceFont = Font.CreateDynamicFontFromOSFont("Source Code Pro", 12);
    static object internalOnGuiDelegate;
    static bool useCustomFont;

    [MenuItem("Tools/Hack Console Window")]
    static void HackConsole()
    {
        if (internalOnGuiDelegate != null)
        {
            return;
        }

        // fetch types/fields
        var consoleWindowType = typeof(EditorWindow).Assembly.GetType("UnityEditor.ConsoleWindow", true);
        var parentField = consoleWindowType.GetField("m_Parent", BindingFlags.Instance | BindingFlags.NonPublic);
        var onGuiField = typeof(EditorWindow).Assembly.GetType("UnityEditor.HostView").GetField("m_OnGUI", BindingFlags.Instance | BindingFlags.NonPublic);

        // get values
        var console = EditorWindow.GetWindow(consoleWindowType);
        var hostView = parentField?.GetValue(console);
        var onGui = onGuiField?.GetValue(hostView);
        internalOnGuiDelegate = onGui;
        if (internalOnGuiDelegate == null)
        {
            Debug.LogError("Couldn't hijack the console window!");
            return;
        }

        // inject custom delegate
        var dgt = Delegate.CreateDelegate(editorWindowDelegate, typeof(ConsoleHijacker).GetMethod(nameof(HijackedConsoleGUI), BindingFlags.Static | BindingFlags.NonPublic)!);
        onGuiField.SetValue(hostView, dgt);
    }

    static void HijackedConsoleGUI()
    {
        // add buttons or anything else above the original GUI:
        var builtInFont = GUI.skin.font;
        useCustomFont = EditorGUILayout.Toggle("Use monospace font", useCustomFont);
        GUI.skin.font = useCustomFont ? monospaceFont : builtInFont;

        // draw the default internal console GUI
        var delegateType = editorWindowDelegate;
        dynamic converted = Convert.ChangeType(internalOnGuiDelegate, delegateType);
        foreach (dynamic deleg in converted.GetInvocationList())
        {
            deleg.DynamicInvoke();
        }

        GUI.skin.font = builtInFont;
        // add anything else below the original GUI:
        GUILayout.Label("This console has been hijacked!");
    }
}

I procrastinated a bit the other day and searched how to hack Unity's console GUI...
This script allows you to hack Unity's Console GUI to add your own buttons or other GUI components above or below the original one.
In this example I added a toggle to enable using a monospace font for the console (note: this is now an option in Unity 2021+).

Works in Unity 2020.3 but heavily untested, and you will have to reinject the custom method after each domain reload (although this can likely be automatized).