Caustic: TFT Set 18 trait
Caustic is a single-unit trait in TFT Set 18: it belongs to Kog'Maw and is active as soon as Kog'Maw is on the board.
What Caustic does
Caustic damage 30% Shreds and Sunders enemies for 4 seconds. Shred: Reduce Magic Resist Sunder: Reduce Armor
From Riot's game data, with the latest patch notes applied; the exact numbers can change between patches.
Kog'Maw