Nothing can be done
snoopygirl asked for a oneshot of Henry summoning Emma using the dagger in their secret place. But she has already subcommand to the darkness.
Henry tried to steady his nerve as he held the dagger shakily in one hand. The sea breeze whipped around his face as he sat on the rickety old wooden play castle.
"I summon thee- Dark One." He croaked. Almost instantly, Emma appeared in a cloud of purple smoke.
"What do you want kid?" She snapped. Henry felt like his torso had both gone hollow and been filled with icy cold water. His mom didn't love him anymore- the darkness had taken it away right now.
"I want you to love me- be my mom." Henry said- tears prickling behind his eyes. Emma gave an evil smirk.
"Oh kid, not even that dagger is powerful enough to make me love you. Not you or anyone. Don't you know? Didn't you see with your grandfather? The Dark One cannot love- not really."
"You're my mom!" Henry screamed. "I just want you back!"
"Well we can't always get what we want!" Emma snapped. Henry flinched- Emma barely ever snapped. Now every time she spoke her voice was cold and near unrecognisable. Emma sighed, and Henry could see how mad she looked.
"This is pointless. Give me that." Emma snapped. Henry could see that nothing he could do would make his mom love him right now, so there was no point in holding onto the dagger. He handed the dagger back to Emma and as soon as it was in her hand she disappeared- taking all Henry's hope with her.