Genjutsu are techniques that are employed in the same fashion as ninjutsu, requiring chakra and hand seals. However, the primary difference between the two is that the effect of genjutsu is illusory, creating chakra imbalances in the victim's brain, causing a disruption in their senses. Depending on the user, these techniques can pretty deadly. Many try to release genjutsu, but it is why harder to notice and then dispel when a skilled user performs it. That is why Shenron created this technique. While having the shinigami inside him allows him to be unaffected by genjutsu, similar to a Tailed Beast and it's jinchūriki, Shenron does not entirely trust Shinigami to get him out of every genjutsu situation.