Originally Posted by Fat FlareBlitz
Super Fang takes any defensive potential counters to 44% health immediately - Umbreon faces a high chance of being KO'd with Super Fang -> Blizzard in hail conditions, for example.
Two things. First, it would bring a Pokemon with Leftovers down to 50% after they healed, such as Umbreon. Second, in almost any scenario, if Super Fang followed by another move KOs, then two of the same move would also KO, or at least certainly get close. When you factor in that Walrein does less damage than other special attackers with Water and Ice moves, he falls out of favor completely. Since Blizzard does 40% max, Umbreon would be left with 10% health with no hazards, which means it survives Hail.