With Fiora back in your party, it should be not much work to head back down Tephra Hill and fulfill all the lingering quests you have for the areas of Tephra Hill and Colony 9. Then it’s time to resume the story quests, by heading into Tephra Cave itself. First, though, you should follow the Heart-to-Heart conversation here.
This talk is between Shulk and Reyn, reminiscing over how they’re friends despite their differences, and how it is they manage to get along. After a few moments just considering their friendship as a whole, Reyn reminds Shulk of ‘that time...’ He’s speaking of a fight the two had a long time ago, though neither of the friends can remember what the fight was actually over. After a bit of banter, Reyn points out that he’s kind of an oaf, which Shulk points out may have been what was said to start the fight back then. The two share a bit of amusement over it, and Reyn asks Shulk if he thinks about their differences and friendship sometimes. As any good friend would, ‘of course’ he does- granting him complete success in this Heart-to-Heart as well.
With that out of the way, it’s time to enter Tephra Cave. The cave is very short and narrow, but it includes a curious sort of an ‘overpass’ that allows you to pass over the middle section of the cave instead of through it. This may be very important- lurking in the main path, underground, is a positively immense, named Caterpile that will rip you to shreds if you aren’t prepared for it. Taking the upper path has the added advantage of providing you with several more opportunities to gather collection items for the cave. Whether or not you choose to face down Mining Patrichev, the rough-hewn cave is quickly gotten through with or without minor diversions- and so the trio reaches the entrance to the Mag Mell ruins. Make sure you keep an eye on the area around you and the icons floating over the monsters- most of the monsters here bear the ‘eye’ symbol and will attack you if you’re not considerably more powerful than them.
On arriving at the ruins, the camera leaves the group for a moment to pan around, taking in the first ‘room’ of ruins, a two-tiered area with a ramp leading up and a number of strange blocky obstacles on the lower floor. This area is mostly not more dangerous than the Tephra Caves proper, though the one truly challenging fight is far nastier than the battle you may have had with Mining Patrichev if you are not prepared for it. If you feel like you’ve been having a hard time so far in Tephra Cave, it would be a good idea to use your map for some Landmark travel back and forth from Tephra Cave to Colony 9 so you can grind out a level or two.