Chansey

Chansey is a staple in the RBY metagame, present on nearly 100% of competitive teams. The reason for its extreme popularity mostly lies in its gargantuan special bulk neutralizing Psychic-types, an otherwise incredibly difficult task without using Psychic-types of your own, as well as its ability to completely wall other special attackers like Lapras. It does not perform as well against physical attackers, however; strong hits from the likes of Snorlax and Rhydon can threaten an easy 2HKO, so Chansey must be wary of these threats whenever entering the field, although it does possess tools to ease these matchups despite its generally innocuous offensive presence. Nonetheless, Chansey is somewhat of a requirement in any RBY team due to the risks you would take against Psychic-types without it.