Twintania is a boss and one of the Demons of the Rift in Final Fantasy V guarding the pathway to the crystal zone atop the dimensional castle in the Interdimensional Rift. It has two forms: the regular form, and the second form that appears after it utters "Charging Gigaflare!"
An easy way to defeat Twintania is to do nothing but heal until it starts charging Giga Flare, then cast Break or Odin.
A simple strategy which will result in little to no damage to the party, as well as killing Twintania quick enough that it will not start charging Giga Flare, is to equip the party with Reflect Rings and the Black Mage class and have every character multitarget high tier elemental spells on the party. The spell will reflect on the boss four times. Twintania counters with Mega Flare, but it will also reflect.