Star Wars Rebels is coming back Feb. 19 for the last half of its fourth and final season. Before that happens, you may want to brush up on your esoteric Force lore — and I’m not talking about the Jedi or the Sith …

From the midseason trailer released last week, it looks like Rebels will be revisiting some really out-there concepts introduced in executive producer Dave Filoni’s earlier Lucasfilm series, The Clone Wars.

In the middle of the Clone Wars’ third season, a curious three-episode 2011 story arc explored some rather arcane secrets of the Force that transcended dark and light. Known as the “Mortis trilogy” or “Mortis arc,” these episodes — “Overlords,” “Altar of Mortis” and “Ghosts of Mortis” — took Obi-Wan Kenobi, Anakin Skywalker and Jedi Padawan Ahsoka Tano on a wild adventure in an ethereal realm known as Mortis after an encounter with a mysterious monolith in space.

In this bizarre new world, a light-side Daughter clashes with a dark-side Son, with a stern and wise Father keeping the balance. All of our heroes are tested by visions of the future and voices from the past — but none more than Skywalker, who gets a dose of destiny dropped on him that may surprise you.

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Strange encounters on Mortis. (Lucasfilm)

Why is this Rebels-relevant? Because it looks like the Father, Son and Daughter are coming back — or, at least, the images of them are.

There’s also an ethereal-looking realm teased in the trailer, apparently in conjunction with a “convor,” a birdlike being that has appeared several times in both series, and was all the rage among Star Wars fans before The Last Jedi’s Porgs ruled the roost.

Animals have been a big part of Rebels, from Loth-cats and now Loth-wolves to convorees, as they’re known in the plural.

The avians seem to be omens of a sort, or maybe even something more. Filoni once described them as messengers and observers, telling IGN in 2016: “It is definitely something. And I would suggest – I would rather have fans debate – but I would suggest to say that whatever that thing is an avatar of has actually appeared in the animated Star Wars universe before.”

The “Expanded Universe” of Star Wars novels picked up the Mortis threads, tying them to an ancient race of “Celestials.” Those stories are now not considered canonical and have been rebranded as “Legends,” although some EU concepts, such as Imperial Grand Admiral Thrawn, have found their way back into canon through avenues such as Rebels.

If you haven’t watched any of Clone Wars, go ahead and watch the Mortis saga anyway — it kind of stands apart in that series, and it will better prepare you for what may lie ahead in Rebels. And Clone Wars is amazing anyway, so why not just fire up your Netflix-connected device and watch it all there while you still can?

Read more of Nerdvana’s coverage of Star Wars Rebels Season 4: