After Cell was so easily defeated by Goku in Dragonball GT, he vowed to gain enough strength to outmatch everyone who sent him to hell. One by one he absorbed every person ever sent to hell, starting with Frieza. He became a shadow figure with no features except red glowing eyes.
While Goku is traversing the Dragon Realm he is suddenly attacked without warning by Shadow Cell (who is essentially the very essence of hell combined into a single being). Even with all of his training, Goku stands no chance against him, even once he transforms into a Super Saiyan 5.
Cell's power is so formidable that he seems to bend reality to his will, forcing Goku into pain without so much as flinching. During the battle the two destroy multiple planets, as Cell smashes Goku around hundreds of thousands of miles through space, eventually leaving Goku no choice but to flee.
As Goku is attempting to flee, with Cell quickly gaining on him, he is left with no choice but to once again turn and face him head on. But just as Cell approaches for the kill, he hits an invible barrier, trapped by the confines of hell. Try as he might Cell can not breach the barricade and Goku proceedes to insult him childishly before leaving him in the middle of nowhere to continue his journey through space.
Cell eventually escapes hell by tearing a hole in the universe and travels to Earth via instant transmission, where he finds Goku and attempts to kill him again. After a short battle Cell begins to create a black hole on Earth creating ripples across time and space, (essentailly creating Evil Goku in the process) and as a last desperate atempt, Goku holds the black hole in his hand, and performs an instant transmission punch teravelling faster than the universe can comprehend, hitting Cell through the black hole and across several other dimensions. Knocking him into an alternate reality, ultimately removing every soul in hell from existence.
Shadow cell had decimated entire worlds in the dimension he was trapped in. He heard a familiar voice from behind him. When he turned around Bowen stood I front of him. " I will crush you like the whelp you are!" Cell roared at his foe. The two rushed towards eachother causing sonic booms. Bowen eventually decimated cell by going legendary ascended super saiyan 3 ( a form only he could use) and fired his crimson nova kamehameha blast, completely obliterating cell.