The pendant reacting to elf blood
The Elixir of Life refers to a legendary magical potion made with elf blood. It can bring back anyone from the dead or similar conditions like petrification.
After his wife Queen Dagmar was petrified by a potion, King Zøg began a quest for the elixir of life in hopes of restoring her. Throughout the first 10 episodes of the series, Zog's quest for the Elixir and Sorcerio's attempts to create this elixir using Elfo's blood are a recurring theme. Eventually, it is discovered the elixir already exists and is contained within the Eternity Pendant. However, for the elixer to work, a drop of 100% pure elf blood is needed.
If the Pendant is filled with pure elf blood, it will grant immortality to whomever wears it. If the wearer is already dead, the Pendant will reanimate their body back to life. If filled with blood of a half elf such as Elfo the pendant is capable of healing the wearer but the effects are temporary. An example being the pendant ridding Prince Guysbert of his headache but didn't heal the stab wound in his head, as he ultimately died seconds later.