Entei is now avaiable as limited time raid boss for the next 3 months. For the first month, from August 31 to September 30, he will be available in the Continents of Africa and Europe. He will then switch regions on September 30 and October 31, so stay tuned to find out where he will appear next.
Tips and strategies
Effective attack types
Being a Pure Fire-type Pokemon, Effective type against Entei include Water, Rock and Ground-types. These are all very common types, making it very easy to find a Pokemon to use against Entei.
All of Entei's attacks are Fire-type, meaning Rock, Water, Fire and Dragon-type Pokemon are all resistant to it. With Water and Rock being fairly common, it will be easy to find a Pokemon that can resist Entei's attacks. But avoid using Grass, Bug, Ice and Steel-type Pokemon, as they will be weak to Entei's attacks.