Mr. Mime is almost like a mini-Alakazam—although he has a better base Defense stat than Alakazam, its lower base HP stat counteracts it, and its lack of Recover greatly diminishes its usefulness. If you play in an UU environment, Mr. Mime is very useful since Poison-types are frequently used there. However, using it in OU is not recommended.
Balance. This team can combat any type of pokemon. Anchored by Mew, who is obviously a beast, mutliple pokemon have moves that are Super Effective against many cross-types of pokemon. Any pokemon you send out we will be able to counter with, and thats what makes this team so deadly.