From personal experience, I think that Raticate belongs in D Rank. It is similar to Kanghaskhan: it's outclassed by Tauros, but it can be used if you simply don't want to use Tauros. Raticate also has a personal move, Super Fang, that will always rip 50% off the opponent's health, even on Gengar (so like full health goes down to half, and 80% health goes down to 40% health). However, it is very fragile, and wants faster opponents, especially Starmie and Alakazam, removed. However, unlike threats like Charizard and Electrode, Raticate is guaranteed to cause problems for at least one Pokemon on the opponent's team. It puts a lot of pressure on Exeggutor, Lapras, and Snorlax, giving them problems switching in on it, it has Bubblebeam to deal with Golem and Rhydon, and Gengar is too afraid of Super Fang to switch in. Its base 97 speed is also not that bad, as it outspeeds Jynx, and it is enough to keep her from attempting to switch in on a Bubblebeam. Overall, Raticate is not the best Pokemon around, but it is definitely D-Rank worthy, as has enough to keep it with being groupped up with shitty mons like Poliwrath and Raichu that have no place on an OU team.