
It's a good idea to use it, as you will be attacked by Bandits and Spritzers throughout your trek. Follow the path up the steps, where a Save Point lies just to the right. Once outside, cross the bridge - Terra will be spotted mid-way - and enter the mines. Before leaving, check the clock in the front room for an Elixir. After a quick chat, some guards start knocking on the door, which means that it's time to get the hell out of dodge. Terra wakes up in a kind stranger's home, her only memory being her name. Going over to it will trigger a cutscene that should probably raise a few questions. With Ymir and the Narshe guard out of the way, the trio is now free to approach the frozen esper. Use the free time to heal your party members as needed once Ymir reemerges, continue to pelt it with Missiles and Fire Beams, and it will be dead in no time. Use Terra's Magitek Missiles and Biggs' and Wedge's Fire Beams to do as much damage as you can before the creature retreats into its shell. Ymir mostly uses physical attacks in conjunction with Slime, which will slow your characters down, but this shouldn't be too much of an issue.
