Back in the days of yore, when things were simpler, one could easily "Send to Motion" from Final Cut Pro and do whatever effects and compositing work their hearts desired. Once FCPX was released in 2011, the "Send to Motion" command that many took for granted, was mysteriously missing without explanation.
Obviously, many things changed when FCPX replaced FCP7, but while FCPX was a new app from the ground up, it certainly seemed to be much more of a "blood relative" to Motion 5 than the previous iterations of both apps.
As has been stated by many experts, FCPX literally has a version of Motion 5 running underneath its "skin". This is demonstrated in the many similarities in form and function between the two apps, as well as things like the "Open a Copy in Motion" option when an effect is right-clicked in FCPX as well as the "Publish to Final Cut Pro" option that is present in Motion for creating templates for use in FCPX.
This is why it continues to blow my (and many others) minds that there is no direct "Send to Motion" command, even 5 years after the release of FCPX.
1. Export your entire project from FCPX to Motion using the Share Menu. This will basically translate your whole project to Motion. This method will use equivalent effects like crossfades, as well as feature support for some third party effects like Colorista, etc.
2. The other option will be to export a single clip or section. Since exporting XML of regular clips is not supported in FCPX, you will create a compound clip of the clip/section you wish to bring in to Motion 5, and then export that as an XML file to then be translated to Motion in the Xsend Motion app.
There is no way (currently) to "send back" or round-trip to FCPX, a la Adobe's "Dynamic Linking", although a re-import of the clip in to a FCPX timeline, is easy enough.
Obviously, there will be people who argue that this is something Apple should have taken care of on their own a long ago, as a basic part of the app's functionality. Especially since it already existed for years prior to FCPX!
I personally prefer not to hold my breath for Apple to get around to these things, so it's nice to be able to rely on the many third party developers that create these "How have I lived without this?" kind of apps and add-ons that make up the massive Final Cut Pro X eco-system.