First, You need to get and equip Dragon Slayer sword(5% chance) then, You need 3 Armor Pieces( 15% chance ) and 5K stats in Sword, Defense and Strength; once you have these things you can talk to the Struggler who for 35,000 gems and your Armor Pieces will unlock Dragon Slayers transformation.
This is found on the new island, Midland, in the multiverse sea. Buffs: 2.1x global damage, 1.5x sword damage, increases speed by 3x, 1.5x damage reduction and gives you 5 dodges
the Struggler is located in the centre of the island.
Accessories[]
—Warriors Cape
● Haki: 800
● Sword: 1500
●Strength: 1000
●Defense: 650