Mephisto’s documentation is seriously lacking, but what can you expect from a small development team with no funding behind the app. Most of the links I followed were to the Mephisto Google Group. I took this snippet from one particular thread:

 <ul>
 {% for month in section.months %}
     {{ section | monthly_articles: month | assign_to: 'monthly_articles' }}
     <li>
     {% if monthly_articles %}
         {{ section | link_to_month: month }} ({{ monthly_articles | size }})
     {% else %}
         {{ month | format_date: 'my' }}
     {% endif %}
     </li>
 {% endfor %}
 </ul>

But this would still spit out months with no posts. We can’t have that! So, I turned it into this:

{% if section.months.size > 0 %}
<ul>
    <li class="head">Archives</li>
    {% for month in section.months %}
    {{ section | monthly_articles: month | assign_to: 'monthly_articles' }}
        {% if monthly_articles.size > 0 %}
            <li><span class="right">{{ monthly_articles | size }}</span>
            {{ section | link_to_month: month }} </li>
        {% endif %}
    {% endfor %}
</ul>
{% endif %}

Much better! Now I have this: