In my quest to try and make some soot-stained arrows, I've been on the hunt for Young Firecats to harvest their teeth for the arrowheads. However, they've been a real pain to track down. According to elanthipedia, they should spawn in the [Cavern of Fire, Stalagmite Maze], but I hunted there for a while and only came across Supple Firecats. It also mentioned that they spawn out in the Gate of Souls, out off from the NTR, but I didn't see any during my hunting in either [The Fangs of Ushnish, Lava Field] or [Temple of Ushnish]. The only place I managed to come across any were out in [Skeleton's Crook, Ruins], were I came across two over the course of about 45 minutes amidst plenty of Fire Maidens/Sprites and Immature Firecats.

Is there a particularly good place to hunt these? Or is it really just Skeleton's Crook now with an abysmally low spawn rate?

It looks like they were limited to a total population of 2. They will still be rarer, but should be seen slightly more often.

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NaOH+HI