This is Hiccup's shield used to defend himself from future outcast attacks.
It first was made of wood with a center hube with a painting of Toothless on it but it is now made with Gronkle Iron which made it stronger and lighter.
Besides deflecting attacks it has its own surprises.
The center contains a retractable cable which can be fired off like a grappling line which can entangle an enemy or hook something in a distance but how far it can reach is unknown.
The second weapon is a catapult on the side that can launch weapons or surprise an enemy at close range.
Then Hiccup coated the enitire shield in Gronkle Iron and now it transformes into a cross bow.