Thornmaiden: TFT Set 18 trait
Thornmaiden is a single-unit trait in TFT Set 18: it belongs to Zyra and is active as soon as Zyra is on the board.
What Thornmaiden does
Your team gains 5% Durability, increased to 10% if 6 or more Zyra plants are alive.
From Riot's game data, with the latest patch notes applied; the exact numbers can change between patches.
Zyra