When you play as buggy in grand adventure go to the Shipwreck Graveyard - the second shipwreck on the left is Shanks! Defeat him and his crew of Lucky Roux, Beckmann, and Yassopp and you unlock Shanks for grand battle mode!
When you go to Albasta you'll see a shipwreck - go there & fight Shanks, then go to the graveyard of ships fight Mihawk and win - he'll give you a compass that says Skypiea on it. Go to Jaya Island, then then go in the whirlpool - it will turn into a Waterspout & shoot you to Skypiea
Chaser - In Chaser's adventure mode, level him up until you have his secret attack to unlock him.
Eneru - Recruit him in Crocodile's adventure mode, and win a battle with him.
Kuina - Recruit her in Chaser's adventure mode, and level her up until you use her secret attack to unlock her.
Mihawk - Recruit him in Chaser's (Smoker) adventure mode, and win a battle with him.
Mr. 2 Bon Clay - Recruit him in Crocodile's adventure mode, and win a battle with him.
Nico Robin - Recruit her in Luffy's adventure mode, and win a battle with her.
Ohm - Recruit him in Crocodile's adventure mode and win a battle with him.
Trace (Ace) - In Buggy's adventure mode, you can recruit him in Drum Island. Win a battle using him to unlock him.
Shanks - Recruit him in Buggy's adventure mode, then win a battle using him
Zeff - Level him up and unleash his secret attack in Chaser's adventure mode to unlock him.
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