Snorlax vs Mewtwo

It's listed as a "tank" counter, which means it will do OK with Lick/HB and last a while against anything not Focus Blast. Fine as an anchor, but hopefully you're never in a battle long enough to have to use him.

It's especially tanky against shadow ball.

I just wanted to ask the same Question.
When I look at the Counter list I have following Pokemon which seem reasonable:
1 Pinsir
1 Dragonites: DT/Hurricane
2 Gyarados: Bite/HP
3 Snorlax: Lick/HB
.................................
1 Dragonites: DB/DP
2 Gyarados: Dragon/Dragon moves (legancy)
Gengars with wrong movesets. (TMs?)

What's your opinion is my lineup in this order okay? Or would you use another TM? Unfortunately I have no good Tyranitars so far. :-(

Assuming your snorlax has lick/hyperbeam and is level 37 with 15 atk iv, its kill speed against mew2 would be on a par with that of a level 26 15 atk iv bite/crunch gyarados. Not too shabby in my opinion (especially when additionally taking into account survivability) if you already have such snorlax at hand and are not swimming in high level top counters.

What about Lick/BS?

First week my wife fought in a group of 13 weak/mid level players against Shadowball. She is level 30. She had 2 2400 Tyranitars, 2600 Dragonite, 1850 Houndoom and two 2400 L/HS Snorlaxes. Took the group 160 seconds, she was one of the few that survived.