Question

What grass type Pokemon is fast, has high sp defense and defense and can learn solarbeam and sunny day?

Answer 1

Venusaur.
DW Venusaur gets the ability Chlorophyll, giving it double speed.
Base 80 HP, 83 Defense, and 100 Special Defense makes it pretty bulky.
However, it should be used with a Drought Ninetales, not with Sunny Day.