I am currently using Mymind and Agenda together. Agenda has the ability to share with Apple Notes. It would be great if it could share the Mymind.
Agenda should be able to share with any app that can accept one of the formats it can make.
Generally, Agenda can make text and rich text, as well as PDFs and other document types, and links. If Mymind has registered to accept any of these types, it should be possible to share that type to Mymind.
If you think it should work, because you can share from other apps to Mymind, let us know the details and we can investigate. Otherwise you probably need to ask Mymind to make a sharing extension.