5 minutes ago, Hiemfire said:And there is nothing in Canon excluding strong darksiders from becoming force ghosts. Heck, "light"siders had no clue how till Qui'gon figured it out.
There is, yeah - the last few Clone Wars episodes dipped into that a bit. It's a Light Side only power - although some Sith had some ability to impress parts of their consciousness into objects (IE., Sith Holocrons or Lord Momin's mask), which could be a closer alternative to what is going on here. Would also explain the Endor connection.