The mystique Twitter widget was broken and needed a fix.
The new widget does rely on a “widget id”, provided by twitter.
Here is how to use the working widget that Mystique 2 embeds :

First, you need to go to https://twitter.com/settings/widgets/ and create a new widget to get the “widget id” from the code twitter then provides: data-widget-id=”1234567890″.

Then you can go to the Appearance/Widgets section, drop the widget and fill in the details.

We feel it’s a pain in the a**, but twitter doesn’t leave any choice: The old API is no more available, and this is the only legal solution we are aware of.