Is there a final boss in the bandit dungeon in Viridian? Is there an end? Or is it just a grinder for raising your pets levels?

Yes, there is a final boss, with 3 mini bosses before that ( you'll have to solve a puzzle each for the mini bosses). Once you defeat the final boss and open the chest at the end, the dungeon ends, and you can't play it again until the next day.

Umm. I have defeated Blaze and the girl with the Vulnyx puzzle. So there's one more miniboss and the final boss?

Yep, that's right.

The next puzzle is kinda hard if you don't know to look out for it... You should have seen some text by now where you notice x amount of chest/figures/pets or something, and Jinxie was like "I don't know if that means anything"... You'll have to remember those numbers, 3 of those, to unlock the 3rd mini boss. If you missed it, you'll just have to skip that boss. Most people miss that on the first dungeon run.

Then after that is the final boss, which you won't need to solve any puzzle for to battle. Final boss is Talon with 2 pets.

Ok. I'm battling Zealia and Prism. Will I completely restart if she defeats me?

I'm not sure, since I've not lost in the dungeon before... I wouldn't think so though, since you can "skip" the mini bosses if you can't solve the puzzles... It just means you won't get a chance to get mythical equipment from them is my guess.

So I'm not sure if you lose whether you'll be able to move on, or you'll have to fight the same boss again..

Final boss must be defeated to complete the dungeon though.

The only battle you would restart is the battle you were defeated in. So if she beats you, you start from right before you started battling her.

Does that make since?

Yep. I actually just figured that out. Thanks guys!