Lucil: Lady Yuna, if I may?Yuna: I’d be honored.Lucil: The honor is mine. Please, be gentle.Lucil and Yuna
Lucil's attacks are mostly physical but she can also perform an attack called Harbinger, which causes Doom. The only way to counter that is to either defeat her quickly or use Ribbon, Ailment Def. (e.g. with certain captured fiends like Omega Weapon and Machina Leader) or the Bitter Farewell Garment Grid and pass through the yellow gate for Doomproof. Lucil uses elemental items, as well as Gold Hourglasses to slow down the party, Chocobo Feathers to speed herself up with Haste, and Light and Lunar Curtains to bestow Protect and Shell on herself, respectively. As her HP runs low, she can restore 1,000 HP with a Hi-Potion.
Using Force of Nature or any elemental absorbing/nullifying accessory, dressphere, or Garment Grid helps as well, against Lucil's elemental items. Combining Ribbon/Doomproof/Ailment Def. with Force of Nature pretty much ensures victory, as the only way for Lucil to defeat the player is to physically attack, which is not much of a threat.
Lucil can be recruited anytime in Chapter 5 with a Trap pod SP in Mushroom Rock Road if the player handed over the Awesome Sphere to the Youth League. She retains her signature Harbinger attack.
Lucil is an optional boss in the Fiend Arena in the Youth League Tournament. She is fought either by by herself, or together with Yaibal and Elma. Here, she is much tougher, as she has access to Heartless Strike, which can KO a character. In addition, she can attempt to defeat the entire party with Shin-Zantetsu and can inflict massive physical damage with Fireworks.