Is there an adverb for the root adjective mediocre?

There isn't a single, universally accepted adverb directly derived from "mediocre." However, you can use several options depending on the specific nuance you want to convey:

Formal Options:

* Mediocrely: This is the most direct adverbial form, though it's not commonly used.

* Moderately: Indicates something that is neither outstanding nor poor.

* Passably: Suggests something adequate but not exceptional.

* Adequately: Implies meeting minimum standards.

Informal Options:

* So-so: Used to describe something that is neither good nor bad.

* Middling: Similar to "so-so," implying average quality.

* Fairly: Can be used in a neutral or slightly negative way.

* Just okay: A colloquial expression indicating acceptable but not impressive.

Example:

Instead of saying, "He performed mediocrely," you could say:

* "He performed moderately well."

* "His performance was fairly good."

* "He did just okay."

The choice of adverb will depend on the specific context and the degree of negativity you wish to convey.