[edit] Do I need Final Attack or Not?

Many warriors wonder, what's final attack, and why should I have it? Final Attack is much like an MP free Power Strike. When it is maxed it has a 60% chance of following any attack with a damage of 250%. Now the real question is "Do I need it?" Well if you are a Fighter, FA is almost required. It is fast MP free and powerful. With a Page it is a good idea to max FA. At 3rd job the page gets elemental skills that work for a certain amount of time. Since FA is fast you can get a few extra hits with each element.

Final Attack diffuses its damage with Slash Blast. Basically this means instead of doing 500, 500, 500 with Slash Blast you'll find your attack broken up with 500, 100, 500, 100, etc... whilst it's still free damage, and you'll level faster with Power Strike getting the free fast FA off it, it does mess with Slash Blast. It apparently goes down in damage as it spreads through the mob too. With SB, FA each following monster will receive 50% of the damage(up to 6 monsters). ex. 1000, 500, 250, 125, 63... thats why when you SB a mob the last 1 or 2 need an extra hit.

Still, it's recommended you get it because there's not much else and it saves MP. Adding to the confusion, it is possible for the first monster hit by a slash blast final attack to take more damage than a regular slash blast is capable of doing. It seems capable of doing 30% to 40% more damage than regular slash blast. There isn't a real reason for a fighter NOT to get it, because you can easily max all your skills as a fighter (as long as you pick either axe of sword) and it will GREATLY increase leveling speed if this skill is maxed.

Final Attack will not work with 3rd job skills. It is only activated with Power Strike and Slash Blast.

http://strategywiki.org/wiki/MapleStory/FAQs