Onatar's Shroud

Wondrous Item - Rare - Requires Attunement
A long heavy cloak of red and black wool, when the wielder readies for action, it blazes with heat and smoke and readiness for battle.
When a creature attuned to this item rolls initiative, the wearer may declare they are using the shroud. On their first turn of combat, they gain an extra 30ft of movement, and when their first turn ends, the cloak erupts in embers and smoke - all creatures within 10ft of the wearer must succeed on a DC14 Dexterity saving throw or take 3d6 fire damage, or half damage on a successful save.
After using the shroud, it