There are several ways in which custom plugins that are not part of TiddlyWiki's plugin library can be installed when using TiddlyWiki under Node.js. (See Installing a plugin from the plugin library for instructions on installing plugins from the library).
tiddlywiki.infoby their name (e.g.
pluginsfolder within the wiki folder
pluginsfolder of the repository. This is only recommended if working with a forked copy of the repo. It is not recommended if TiddlyWiki has been installed with npm because npm is liable to overwrite the installation when performing an update
Note that including a plugin as an ordinary tiddler (e.g. by dragging and dropping a plugin into the browser) will result in the plugin only being active in the browser, and not available under Node.js.