1. The Shiki Fuujin is a sealing technique of the Uzumaki clan, which can trap the opponent's soul inside the Shinigami. It was used to seal four Hokages and the half of the Nine-Tails, as well as Orochimaru's arms. However, Orochimaru eventually managed to release the seal, demonstrating his mastery of advanced techniques.

2. The Edo Tensei, a forbidden jutsu used by Orochimaru, is the ultimate pursuit of immortality. Once selected by Orochimaru and under the Edo Tensei, one is essentially dead. Despite its risks, Orochimaru's mastery of such technique showcases his advanced skills.

3. Jugo's Kekkei Genkai, the Curse Mark, is terrifying.

Jugo can extract one's heart and replace it with his own, granting himself immortality. However, if Jugo takes someone's heart, they will surely die. Unfortunately, Jugo's formidable powers were ultimately defeated by the protagonist, Naruto. 

4. The Shiki Fūjin Kiss is a special technique exclusive to Tobirama, a grave robber. It allows him to absorb an opponent's chakra through a kiss. If one is enticed and forcibly kissed by Tobirama, the outcome could be fatal. Fortunately, Tobirama targeted Naruto's shadow clone, avoiding a disastrous result.