Krokodil is an impure homemade opioid drug made from codeine tablets that causes severe tissue damage and can lead to amputation or death. It became popular in Russia as a cheaper alternative to heroin but has dangerous side effects like greenish scaly skin, limb loss, and flesh decay due to ingredients like iodine, phosphorus, and gasoline. Despite its risks, some users in Russia and Ukraine chose to take krokodil due to its low cost compared to heroin and easy accessibility of codeine tablets.