Hi again! I heard that you can find themed pets in lost grove? If so how?

by regular old exploring (or possibly if a nest spawns and you get lucky)
However, the theme spawn chance in the grove is WAY lower than in fest zones (which is understandable, as the rove is available at all times to those who have reached it and grove pets have the grove bonus stats which ups their value)

I'd say maybe consider the chances of finding one about equivalent to finding an enhanced essence while battling/nurturing: really really low

Oh wow, what if i use a lost grove perfume...How much better of a chance will i ahve

well, it doubles the chance that you'll find a theme (though the chances are still pretty low, which is presumably the reason grove perfumes only decrease when you encounter sylesti rather than going down with every enemy like zone perfume)