Season 2

Aren't there actually five? One for Master Chef and another for Treasure Hunter?

I have a feeling that Tarlach was warning us about them.

Do they even have a mascot? As far as I know they don't, so it may just be an add for the skills.

They have a mascot, they just don't have as much in-depth detail on the character's background. Also, the treasure hunter's final design was still being determined when we first saw her, he was originally a female elf. Korea did say that there will be a new storyline featuring the three heroes, and master chef and treasure hunter will also make "an appearance", implying they aren't as important but are still notable. Lets just wait and see what happens before setting any judgements in stone.

This could be me but it looks like they used a Milletian as a model for Treasure Hunter's mascot.

Didn't they do that for all the heroes? Using a player character model as opposed to a nao-esque model? Except in Master Chef's unique case, but the female version uses a female giant.