EnumMaskAttribute.cs

using UnityEngine;

public class EnumMaskAttribute : PropertyAttribute
{
    public EnumMaskAttribute() { }
}

EnumMaskDrawer.cs

using UnityEditor;
using UnityEngine;

[CustomPropertyDrawer(typeof(EnumMaskAttribute))]
public class EnumMaskDrawer : PropertyDrawer
{
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        EditorGUI.BeginChangeCheck();
        int value = EditorGUI.MaskField(position, label, property.intValue, property.enumNames);
        if (EditorGUI.EndChangeCheck())
        {
            property.intValue = value;
        }
    }
}