In the current OU the extreme popularity of Flygon and Heatran on offensive teams makes a CM Raikou sweep almost impossible. While against stall CM Raikou is next to useless with no way of getting around Blissey, Sp.def Heatran, Tyranitar and Bulky grounds etc. But like BKC said, Scarf Kou is a very effective set and the anti lead is fun. Some of Raikou's other options are outclassed e.g. if you're using Dugtrio support then agility Zapdos tends to be a much better sweeper. Choice specs Jolteon outspeeds Scarf-Tar and Starmie, while it also gets baton pass to act a s a pseudo u-turn, while Raikou's extra power isn't really worth anything. In UU: Raikou also ran Cro kou (restalk cm) as immunities to electric attacks are not as common in the tier. I think the fact that Dugtrio trapped basically all of Raikou's counters is what made it completely broken in the tier (although it was a great poke in it's own right). Dugtrio was so common during Raikou's spell in UU that some of the top players even ran shed shell Raikou. At the start of gen 4 I remember seeing it a lot more often and it was commonly used with toxic spikes support as it's main checks at the time were bulky grounds and blissey. It took a really long time before people realized that Raikou sucked.