While Dragon Ball Z and Dragon Ball Super remain some of the most memorable anime of all time, many people forget some of the wild opponents Goku and friends confronted during the first series, Dragon Ball. This is especially true for the Dragon Ball movies, in one of which, Goku combated a vampire named after the Devil who sported a pair of sunglasses.
In the second animated Dragon Ball movie, Dragon Ball: Sleeping Princess in Devil's Castle, Goku and the gang are tasked with rescuing the titular Sleeping Princess. The film is essentially a reimagining of the second arc of Dragon Ball, in which Krillin and Goku train under Master Roshi. But this time, Goku and the gang face-off against the vampire Lucifer, an insidious lord of darkness who has an affinity for fashionable eyewear. How did this slick but silly blood-sucker almost overpower the seemingly unbeatable Dragon Ball hero? Well, it's complicated.
How Strong Was Goku At the Time of Sleeping Princess In the Devil's Castle?
When considering how much Goku struggled against Lucifer in the film, it's important to remember that it took place after the first saga of Dragon Ball. The movie starts with Goku and Krillin seeking training under Master Roshi, who requests they find the legendary Sleeping Princess because, well, Master Roshi is characterized as a dirty old man who lusts after young, beautiful women. However, when they reach Lucifer's castle, they realize that the Sleeping Princess is not a woman, but rather a magical jewel that absorbs moonlight.
This means that at this point, Goku was fairly weak compared to what he'd go on to become. According to the Daizenshuu 7, Goku had a power level of 10 in base form and 100 in his Oozaru form at the time. For the sake of comparison, at the start of Dragon Ball Z, Goku's power level was at 416 without weights on him. Basically, when Goku faced-off against Lucifer, he was an untrained child with a vast pool of untapped potential.
Furthermore, Goku still had his tail. While Goku's tail would allow him to transform into the Oozaru, it was also extremely vulnerable to damage. Multiple times during Sleeping Princess, Goku's vulnerable tail is targeted by Lucifer and his demonic underlings. At one point, Goku saves the Sleeping Princess from Lucifer, only for Krillin to then get kidnapped. Goku returns with the princess, only for one of Lucifer's ogres to bite Goku's tail, leaving him paralyzed and in pain.
As for Goku's Oozaru form, while he does transform in this film he never fights Lucifer using it. Rather, Lucifer has his goons trap Goku in a cell, only for the full moon to transform him into the Oozaru. In this case, it's ultimately Yamcha, Krillin and Puar who stop Goku as an Oozaru by cutting off his tail.
How Goku Almost Lost to Lucifer
For most of Sleeping Princess, Goku is set on a grim adventure to defeat Lucifer but Bulma is the one who spends the most time with the sunglasses-wearing vampire. Lucifer plans on toasting his success with Bulma's blood (the equivalent of champagne) after making use of the Sleeping Princess one last time. He has been gradually charging up the jewel over the course of thousands of years and plans on using it to power a super-laser that will blow up the sun, casting the world into eternal darkness. Vampires, after all, are vulnerable to sunlight -- hence Lucifer's sunglasses. (Goofy, but kind of practical.) In eternal darkness, Lucifer might finally be able to overrun the world.
Goku ultimately can't beat Lucifer on his own. Rather, he needs the combined help of Yamcha and Krillin to stand a chance, and even then, it's a real struggle. Just as it looks like Lucifer is about to kill the three of them for good, Goku unleashes a Kamehameha that, rather than blow Lucifer apart, knocks over the giant cannon Lucifer was going to use to blow up the sun.
In an ironic twist, the power of the Sleeping Princess jewel powers up the cannon just as it falls in front of Lucifer. The blast rips through the villain and his castle. In the end, Goku only wins because he accidentally orchestrates Lucifer's self-destruction. Considering the amount of power that would be needed to blow up the sun, it's likely that Lucifer's cannon generated power similar to that of Vegeta's Gallick Gun, meaning that Goku would have certainly been slain by the vampire if not for that stroke of karmic luck.