エディタ拡張：Inspectorにボタンを表示して対象クラスのPublicメソッドを呼び出す

TargetClassInspector.cs

// Editorフォルダ配下に配置
using UnityEditor;
using UnityEngine;

namespace STYLY
{
    [CustomEditor(typeof(TargetClass))]
    public class TargetClassInspector : Editor
    {
        public override void OnInspectorGUI()
        {
            var target = (TargetClass) target;
            base.OnInspectorGUI();

            var buttonEnabled = Application.isPlaying;
            EditorGUI.BeginDisabledGroup(!buttonEnabled);
            if (GUILayout.Button(("Run method1")))
            {
                target.Method1();
            }
            EditorGUI.EndDisabledGroup();
        }
    }
}