Vivi's Focus increase his magic stats at everyturn , and the effect last for the whole battle even if ko'd so it's a must use ability ( the cap is 99 point of magic)
(Magic x 1.25) So if you have let's say 24 of magic stat turn 1 : focus (24x1.25)= 30 turn 2 : focus (30x1.25)= 37.5 turn 3 : focus (37.5x1.25)= 46,875 If base magic is the correct way to calculate it then it's turn 1 focus (24x1.25) = 30 turn 2 focus (24x1.50) = 36 turn 3 focus (24x1.75) = 42 and so on until the stat reaches 99 once at 99 it will no longer increase so it's better to move to another ability or start using spells
not being sure wich one of thoose calculs are correct i'd give both
In game test magic = 24 Damage to plant type with fire and no stock = 148 and around Damage to plant type with fire and 7 stock (reaches the stat to around 91) = 612 and around basically it's like dealing the damage of 4 turn in only 1
you loose 7 turns to boost the ability but regain the damage of thoose turn in only 2 turns in the meantime you can focus on stealing boss 's items and managing everyone's life
Don't bother using it when in trance , just blk magic instead