What are Mana Pearls for?
In Hack Slash Crawl, you can obtain mana pearls by picking up mana pearls from chests or slain enemies or by selling items.
What are they used for?
Solution 1:
They're basically your score. They're for determining your overall progression for gravestones and for earning certain titles.
Oh, and on some sites with that game you can earn badges/achievements for getting enough. Kongregate is one example.