Acid Canister Harpoons are a type of ammunition in Horizon Forbidden West compatible with only one Ropecaster. While it deals low Impact damage when attached to a target, the canister can be set off by Acid arrows, triggering an explosion that deals high Acid damage and very high Acid buildup.
These can be used to inflict the Corroding state on enemies, which deals minor damage over time and weakens the protection provided by armor plating. Effective against enemies with acid vulnerability.