1. what is it.

2. where can I find it.

1. An arena.

2. Ethernia.



...More seriously, though: it's a special but non-required "challenge" of sorts. Every few hours (I forget the exact cooldown), you can fight the enemies in the arena. Once you beat an opponent, you unlock the next one. They're supposed to get more difficult as you progress (though I'd dispute that in a couple places).

Currently there are lv25 enemies and lv50 enemies. Technically you can use pets at any level up to those points, but... honestly, it's best to just use lv25 and lv50 pets.

As you fight, you earn a special currency called Marks, which can be used to buy a few avatar items, some gear unique to the arena, and venes from the vene shop (the only way in game to get tamed venes).

And it's located in the third town, Ethernia, in the section labeled "The Arena".

Thanks (and obviously im blind)