When taking the Frostfire Powder node in the decoy skill tree the description states that its damage will scale with cold instead of fire, and that all ignite chance from the decoy tree will be converted to chill. Additionally, ignite related effects will be chill related effects.
Unfortunately, even with Frostfire powder taken, Decoy does not gain a Cold scaling tag, it still scales with fire. This leads to a strange situation where the resulting explosions are cold explosions (at least visually) but they are not powered by cold bonuses. Furthermore, on the topic of ignites, the “On Fire” node does not function with the new behavior. The decoy still lights enemies ablaze instead of chilling them.