Goofs

The Hétszünyü Kaponyányimonyók has both of his eyes when dangling from the edge of the hole leading to the Underworld, but in every other scene he only has a single eye.

Kömorzsoló and Vasgyúró have bare genitalia when wrestling with Fanyüvö (briefly seen when the latter lifts them up), but after they have met the princesses and run to the hole leading to the Underworld to rescue Fanyüvö, they suddenly have pubic hair.

At the climax of Fanyüvö's fight with the Three-Headed Dragon, as the Monyók flies out of Fanyüvö's clothing, the glow effect around his sword disappears for a second or so.

During the fight with the 12-headed dragon, when the dragon grabs Fanyüvö and laughs, it is briefly drawn with 14 heads.

When Fanyüvö plants the fallen tree back into place after his wrestling match with Kömorzsoló, the upper white edge of the background painting can be seen for a couple frames. This isn't visible in the 2019 restoration.

When the three brothers approach the hut, Vasgyúró's hair disappears for a couple frames.

The official English subtitles mistranslate one of the dragons' lines. When the White Mare gets pregnant with her third son, the dragons threaten the giant snake holding the Mare prisoner by saying "If you cannot deal with this, her third son, your life will be over." The subtitles have the dragons threaten the Mare instead of the snake, saying "You cannot provide milk for a third son, and so your life ends here." The translator probably misheard the outdated phrase "ha te evvel" (if you with this) as "a tejeddel" (with your milk).

When the dragons are unleashed and the Griffin wakes up, the star patterns momentarily disappear from its body. In the same shot, as the King tries to protect the Queen, the blue color around them is also missing for a frame.

When Fanyüvö thanks the Goblin for directing him to the griffin, the solid gold-colored clouds on the horizon become see-through for a couple frames.

When the Three-Headed Dragon offers to wrestle Fanyüvö, the glowing aura around Fanyüvö's head appears on top of his body's animation cel for a couple frames.

When Fanyüvö asks Kömorzsoló to stay at the hut, Vagyúró's head and arms become transparent for a couple frames.

Fanyüvö's brothers already know his name and his goals before they have even met. This makes sense in the tales the film was adapted from because there's many other people living around them spreading rumors, but in the film they apparently live alone, in an empty world where there's no rumors.

Most of the dialogue was based directly on old folk tales, but they don't always correspond to the film's events. The 12-headed Dragon accuses Fanyüvö of eating his dinner like in the original tales, even though he does not do so in the film, he only drinks the dragon's wine.