If you're looking to grab Shantotto, first beat Dissidia and collect all of the crystals. Once that's done, Cosmos (our intrepid FFXI Altana-esque character) will remember spending a period of time with Professor Shantotto.
Shantotto will require you to beat the other 10 heroes and then defeat her in battle to unlock her in the store. Once all of that's done, it just requires 1,000 PP to grab her from the shelf and add her to your arsenal.
Shantotto's attacks, as one would expect from the best black mage in Windurst, are all magic spells. She's the fastest mage in the game thanks to her tarutaru speed, and her EX burst attack is a wonderfully direct reference to Final Fantasy XI. As the EX burst continues, FFXI's menu will appear and your enemy will become targeted, requiring you to choose the right spells to form a skillchain. If you're looking for what you should enter: choose Flare, Flood, Burst, Quake, Tornado, Freeze -- the perfect combination of all of the elements to form a level 3 skillchain.
And that's it! Now go out and destroy your enemies with the power of Windurst! Ooooohoohooohoooo~!