Prone is one of the Afflictions in Pillars of Eternity 2: Deadfire. Afflictions are explicitly bundled sets of status effects that can be applied to, suspended, or fully removed from a character. While some afflictions have explicit overriding or exclusivity rules, most afflictions can co-exist with other afflictions.
Prone is a more effective Interrupt effect that knocks a character off their feet, taking longer for them to regain their footing.
Prone Notes & Tips