Grendl was a fairy and Navi's friend. When some strange black oil appeared inside the Old Hollow, a gathering place for fairies, she was trapped by the oil and began to be sucked into it. She saw Navi enter and she called out for help. Soon Navi plugged the hole with a cork, stopping the oil. (The Legend of Zelda - "Dark Triforce: Bleed")
Grendl can be seen bleeding after he got attacked by a giant bird, Link saves him and they become better friends. (Zelda Tears Of The Kingdom "A Fresh New World")