Alakazam

In a generation where Psychic-type attacks are only resisted by the same type, and because its only weakness may as well not exist, it's not surprising that Alakazam is an incredible threat in RBY OU. Alakazam is most commonly seen in the lead slot due to possessing excellent Speed and access to Thunder Wave; it outspeeds every Pokemon that has access to a sleep move, allowing it to immediately cripple them with paralysis. It also has the strongest Psychic in OU by virtue of its excellent Special and as such can heavily pressure its most common checks. This Special stat also makes it a decent sponge for opposing moves like Psychic, though its HP limits this slightly. It is also good at absorbing sleep, since it resists Exeggutor's Psychic. Unlike Starmie, Alakazam doesn't have a weakness to Thunderbolt, which can come in handy for absorbing sleep from the likes of Gengar and Lapras. Alakazam can also prove to be very effective outside the lead slot, maintaining excellent utility against various threats and potentially turning into a dangerous sweeper if its most common checks have been removed. However, it can be difficult to consistently keep Alakazam safe from paralysis; if paralyzed, Alakazam often finds its low Defense being exploited by strong physical attackers such as Snorlax, Rhydon, and Tauros. It's also very reliant on its Psychic, which means it is difficult to break past Chansey. Overall, Alakazam is a regular presence in RBY OU and one of the best Psychic-types available, but its extreme vulnerability to strong physical attacks and paralysis keeps it firmly below the top of the pyramid.