Idea: Rescuing Momma Sprout from Eternal Slumber is only the beginning.
Eternal is pissed that the Sprouts escaped his control, and seeks revenge against both of them.* Despite Pest Sprout's attempts to contain him, Eternal breaks Quest Sprout's shrinking spell and begins plotting a massive attack on him and Momma Sprout.
At bedtime, the Sprouts decide to have regular dreams instead of entering the Dream Realm, because they think Eternal will attack them upon arrival. However, once they fall asleep, they begin having nightmares showing their respective fears. As the nights go by, their nightmares get bigger and scarier, to the point where the deepest fear they both happen to share is shown: losing each other for good, either through physical separation or death.
Meanwhile, it's revealed that Eternal is using his powers to induce nightmares on the Sprouts so that they get scared into entering the Dream Realm, where he will fight them the moment he sees them.
Eventually the Sprouts can't handle the nightmares and go to the Dream Realm. Once he sees that the first part of his plan worked, Eternal transforms the Dream Realm into a place of nightmares where fears come to life, and goes to attack the Sprouts.
What comes next is a very huge battle against not just Eternal, but also a demon army and physical manifestations of the Sprouts' fears.
*And it HAS to be both. Momma Sprout can't be sidelined again just because she was rescued.
I'd have it so that Harpe, Joyeuse, and everyone who helped Quest Sprout appears for at least five comics to help the Sprouts fight Eternal. Lake Queen can be part of it, too!
