Legendary Beasts Trio: Raikou, Entei, Suicune

Much like the Legendary Bird Trio that was released in first generation, a second Legedary Trio was released in the second generation. This trio has since been called the Legendary Beasts Trio, consisting of Raikou, Entei, Suicune. These three creatures are based on both realistic and mythical deities, and were first seen in the Johto Region, trapped in the Brass Tower. And all the three are connected to Ho-Oh and its power.

All three beasts carry with them a backstory, but only Entei and Suicune earned a spotlight in the anime series. Suicune assisted the Guardian of the Forest, Celebi, and Entei, with the help of the Unown, came to life and built a world of fantasy for a relative of Ash Ketchum. Raikou did also receive a special that was separate from the original anime, one focused around the characters Ethan and Kris, but it's wasn't as in the limelight as the others.

Raikou is a fast, special sweeper; Entei is the opposite, being a fast, physical sweeper, and Suicune is the complete opposite of both, being a more defensive Pokemon with slower speed and lower attack power.

#243 - Raikou: Raikou was first available in Pokemon Gold and Silver, where it would roam the region after fleeing from Burnt Tower. It does that same in Pokemon Cystal, running from battling even when you happened to find it. Raikou keeps to this same act in the remakes of the second generation of the game, sticking strickly to the same script. It was also seen roaming in the wild after defeating the Elite Four in Pokemon Fire Red and Leaf Green, depending on the starter you chose. Raikou wouldn't be seen, except through events, until Pokemon X/Y. It can be found when soaring through the sky with either Lugia or Ho-Oh, on the island known as Trackless Forest.

#244 - Entei: Entei is found in the same Games and in the same exact way as Raikou. To a T.

#245 - Suicune: Suciune was obtained in the same way as its counterparts in Gold and Silver, but in Pokemon Crystal and Pokemon Heart Gold and Soul Silver, Suicune received a separate storyline where the trainer would track Suicune from place to place and finally be able to capture it in a specific area. It can then be found in TIn Tower in Crystal and Route 25 in the second generation remakes, respectiviely. In the third generation remakes of the first generation Games, as well as in X/Y, Suicune can be obtained in the same way as both Entei and Raikou.