The third-party DPL (DynamicPageList) extension breaks in MediaWiki 1.26 because the "page" table no longer contains a "page_counter" column. Example:
<dpl> category=whatever addpagecounter=true </dpl>
Error message produced:
Unknown column 'wp_page.page_counter' in 'field list' (localhost)
Ideally, DPL should detect whether Extension:HitCounters is installed and use that table, or it should exit cleanly with a message that "addpagecounter" is not supported.