Sinbad (Adventures of Sinbad)

So in Magi, there are Magicians, and there are Dungeon Conquerors aka King Candidates. Sinbad is the latter, and thus have an ability called Djinn Equipping. At this current canon point, he can equip either Valefor, an Ice Djinn, or Baal, a Lightning Djinn.

And there is a slight element factor to magic in Magi: Djinns cannot be hurt by magic of the same element, and are immune to damage from environmental hazards, instead, any energy they spent gets restored by said element, so it would act as a kind of natural battery

So What does it mean?
A Djinn lends their power to a chosen king that if evoked, allows the King to take on the special ability and characteristics of said Djinn. There's two categories of Equipping.

Weapon Equipping: Where only a fraction of power is used, causing the Djinn's vessel (usually an actual weapon or something that can be used as one like a hair pin), causing the vessel and the user's arms to transform to accommodate the magic going through it.

Full Equip: The person's entire body transform into a humanoid avatar of the Djinn - they will look generally like the Djinn (the wolf-djinn Valefor makes Sinbad a kitsune for example), allowing them to use all their magic, including the incredibly powerful "Extreme Magic" - a spell that takes a long time to cast but can cause extreme phenomenon, such as Kougyoku's extreme magic can create a Tsunami, or Hakuryuu's Belial can sever someone's soul from their body.

( Baal, the Djinn of Wrath and Heroes )
( Valefor, the Djinn of Confidence and Deception )