My Tangrowth knows Sunny Day, Growth, Solarbeam and AncientPower.
I was thinking Sunny Day because it has the Ability Chlorophyll, so it can help Tangrowth with speed and also Solarbeam can be used in 1 turn. Growth In sunny day raises Atk. and Sp. Atk by 2 stages instead of 1. Solarbeam well you know... and then Ancient Power is for coverage against Fire, Bug, Ice and Flying...
Is this good enough??