Ice Coins are now a removed currency that dropped from every mob during the 2018 Winter Event. Once you collected enough, you could purchase gears from Tom the Trader.
It's rarity title was "Event Currency", a 2-star item. When buying a Winter Event item, you saw how many Ice Coins you had on-hand. EVERY mob in the game dropped Ice Coin(s) on death, so they were not hard to obtain.