Level: 13, HP: 1290, MP: 370
Rewards: Hi-Potion (always)
Absorbs: Fire, Resists: Ice
Special: !MP Absorb: Attack x0.5, drains MP from the target
Vulnerable to: Paralyze
Attacks: Attack, !MP Absorb, Blink, Fira
Sketch: !MP Absorb, Blink
Blue Magic: None
Draw Spell: Firaja
BGM: Final Fantasy II Boss Theme A
The Mantis Devil is definitely a diabolical disputant. At the beginning of the battle he will cast Blink on himself, making it very difficult for your physical attacks to hit him. On subsequent turns, he alternates with equal preference between a very powerful physical attack, the irritating !MP Absorb, and a devastating casting of Fira. The onslaught is crushing and relentless; he never pauses to use Blink again, and unlike Azure Highwind, he lamentably has no weakness to Badger's Compression.
What the Mantis Devil IS susceptible to is Ferret's Shriek. It won't often hit, due to Blink, and it won't last very long, due to the Mantis Devil's high magic defense, but it'll give you a turn or two to breathe every so often. Have Ferret spam Shriek until it hits, then let her take a turn or two to dispense healing items while Badger and Ultimecia attack. Once the Mantis Devil is moving again, resume Shriek-spamming. If you didn't have Ultrasonic before this battle, you should afterward.
Ultimecia will, once again, be your main source of damage. Whatever would you do without her? (You'll find out soon enough, but for now, just enjoy it.) The Mantis Devil absorbs Fire, unfortunately, so Firaja is not an option, but Thundaja gets the job done nicely. It'll probably take three or four Thundajas to eliminate this beast, and it will likely drain some of Ultimecia's MP along the way, so be prepared to Draw some MP out of it before the battle's over. Note that if you didn't get Firaja from a Gigas Worm in the Chaos Shrine, you can pick it up here instead.
Badger's time is best dedicated to healing, as Compression doesn't do enough damage and Dia is ineffective. If he has a spare moment while the Mantis Devil is paralyzed, it's time to do some Sketching; 75% of the time, this will restore a bit of Badger's MP, and the other 25%, it'll bless one ally with Blink, which will save Badger a lot of MP in the long run by reducing the number of attacks he'll have to heal from.
In short, Badger should Cure when the Mantis is active and Sketch when it's paralyzed. Ferret should Shriek until the Mantis is paralyzed and then use items. And Ultimecia, as usual, should Thundaja the massive mantodea into next week.
Ferret's confidence in Ultimecia is even more firmly entrenched by this encounter. Badger is more besotted by the moment with his lovely, powerful lady. And Ultimecia is seized by a giant fiery vortex that rips time and space asunder, sending Badger and Ferret spinning helplessly through the Void only to land with a WHUMPF in the middle of a land of darkness and starlight.
...What? Did you think I was joking?