How to Beat Cliff in Pokémon GO

To battle him, you first need a Rocket Radar, which is made by collecting six Mysterious Components dropped by defeating Team GO Rocket Grunts.
GameSpot

Pokemon Go Is Completely Overhauling Its Leveling System In October To Be More Rewarding

GameSpot may get a commission from retail offers. Pokemon Go developer Niantic has announced some big changes to the mobile game, as starting in October, progression is being completely overhauled.
IGN

Pokémon Go Boosting Level Cap and Rebalancing Experience, In First Major XP Change for 5 Years

Pokémon Go is introducing a new, higher level cap and rebalancing the XP requirements for existing levels — though no player will see their current level reduced. The game's current level 50 cap, ...