Gargron

This widget shows all tags that are anime titles as a dropdown menu. It creates a taxonomy called Anime, you only need to tag your posts not in the ‘Post Tags’ box, but the ‘Anime’ box.

Anime Dropdown Widget

This widget shows all tags that are anime titles as a dropdown menu. Using WordPress' custom taxonomies.

Erick Hitter

Creates dropdown lists of non-hierarchical taxonomies (such as <code>post tags</code>) as an alternative to term (tag) clouds. Multiple widgets can be used, each with its own set of options.
Numerous formatting options are provided, including maximum numbers of terms, term order, truncating of term names, and more.
Using the <code>taxonomy_dropdown_widget()</code> function, users can generate dropdowns for use outside of the included widget.
Only use version 2.2 or higher with WordPress 4.2 and later releases. WordPress 4.2 changed how taxonomy information is stored in the database, which directly impacts this plugin’s include/exclude term functionality.
This plugin was formerly known as the <code>Tag Dropdown Widget</code>. It was completely rewritten for version 2.0.
Follow and contribute to development on GitHub at https://github.com/ethitter/Taxonomy-Dropdown-Widget.

Taxonomy Dropdown Widget

Creates a dropdown list of non-hierarchical taxonomies as an alternative to the term (tag) cloud. Formerly known as Tag Dropdown Widget.

Anime Dropdown Widget vs Taxonomy Dropdown Widget