I'm not even sure if this type of question belongs here, but here I go...
What happened to Tangrowth? Tangrowth was OU and fairly common in the beginning, but his usage gradually went down. When Platinum rolled around, I'm pretty sure that Zapdos learning Heat wave and Rotom-H hurt Tangrowth. I don't know if Tangrowth was ever BL at one point, but since the BL and UU combination, I thought Tangrowth would go to UU. I was extremely shocked to find Tangrowth sitting in the never-used tier. What's wrong with Tangrowth? NU is for the Pokemon who usually have 1 extremely bad quality (Slaking, Regigigas) or Pokemon who just can't function anywhere else.
I'm not complaining about the tier list, I'm just wondering what made the decision for Tangrowth to be NU. He seems like a totally viable Pokemon.
And I guess that is another question: the current NU list is tentative, right?
Don't over think it, there is nothing wrong with Tangrowth. He's very usable. He's just NU because he is simply that, never used. His Special Defense stat also hurts him alot, and sunny day is hard to use in OU since pokemon like Tyranitar and Abomasnow run rampant.