I want it to be Timid Natured (+Spe. -Atk.) with the Compound Eyes ability.
There are 25 natures and it can get 2 abilities (not considering HA).
Of course you can use a Synchronizer Timid Pokemon for make easy to come a Vivillion with Timid Nature (50%).
2% without Synchronizer.
50% Nature + 50% Ability for be your perfect Vivillion.
Also here is a list of some Synchronizer Pokemons - HERE
Hope this helps! c: