Imp defenders are only found in Puro-Puro and their function is to attempt to release one of the player's jarred implings whenever they're near them. If successful, the impling respawns and the player's jar is also knocked a few steps away. The defenders' success rate relies on the player's Thieving level, however, carrying Imp repellent will also lessen their chances of releasing an impling. they cannot free crystal or lucky implings.
Imp defenders will shout "Be free!" when they succeed in releasing a carried implings and will only release the lowest-levelled impling in the player's inventory on every successful attempt; therefore, when hunting higher-level implings, it is advised to carry around about 2 or 3 lower-levelled implings, so that if an imp defender manages to release an implings, it isn't a priority one.
Notably, impling defenders' aggression decreases as server time increases, and only resets on an update.[1]