Dragonball Xz, dark TRUNKS Saga, Episode 3 - "Lookout Covered By a Dark Cloud"
This is mostly a filler episode where dark TRUNKS goes over his past and how he came to be.
dark TRUNKS was regular Trunks till he was possessed by Black Smoke Shenron . This happened when Trunks had all the broken Dragonballs together, letting Black Smoke Shenron be at full power. But he can't be free until Shenron is dead, but that can only happen by killing Dende. But Black Smoke Shenron won't die, too, because he's in Trunks's body. That means that only the seal and Shenron will die, and Black Smoke Shenron will be free.
"We can't let you do that..." Goku says as he wakes up.
Everyone then goes Super Saiyan 2 .
"You're dead now." Goku says again.