Underdog Day is available after completing the Saronia Docks. Watch the scene involving the Kupirate moogles and get ready to fight the God of Fire himself!
Ifrit is weak against Ice and Water, so stick to stacks that revolve around those. Here’s the stacks I went with:
Stack #1 – Jiant, Sharquel, Moogle w/ Water learned.
Stack #2 – Jiant, Flan, Bablizz
Battle vs. Ifrit
Hp – 6030
Elemental – +100 Fire / -50 Ice & Water
Hit Ifrit with Watera from Stack #1 and Water/Ice magic from Stack #2. Heal when needed, and make sure you’re always above 200 Hp because Ifrit will throw out a Hellfire every now and again which hits for around 200 damage. Once he’s down, watch the scene and you’ll receive Bomb Core x2