After defeating Viper Tobi-Kadachi for the first time during the main Iceborne quest, go to Seliana's Armorer and talk to her to get the free mission "For Great Evils Great Remedies", asking you to capture a Tobi-Kadachi viper (pictures1and2). Read the section "The Snow Cerberus (★★)to find out how to capture this enemy by dodging their attacks while hitting them with your weapons.
After successfully capturing this monster, you will get a Purifier +, with a doubled duration and allowing you to place a fumigator that cancels afflictions and plagues (picture3). This equipment will be one of the most important in Iceborne, capable of removing type afflictions at any time: poison, sleep, freezing, etc. (picture4)