Boss battles usually cannot be won by just attacking. Each Boss has a particular attack pattern. Once you learn them, you can use safe times and angles to attack. Consume potions and use revive scrolls during Boss battles instead of more typical battles.
Classes
The Warlock and Gladiator are considered melee fighters. The Warlock is focused on damage while the Gladiator has more defensive abilities because of his shield. The best ranged class is the Barbaress, who can throw her axes. Although you will level up each character individually, you can switch between as desired at the "Game Settings" menu.
Gear Score
Your Gear Score represents the overall power of your character and is a total of the individual Gear Scores of your currently equipped weapon, armor and accessories. Each level has a recommended Gear Score, and you may not be allowed entry if you do not meet a minimum requirement. To increase your Gear Score, obtain better equipment from drops or tributes. Items with a higher minimum level and of higher rarity usually have higher Gear Score values. You can fuse unneeded items to improve items you wish to keep to slowly increase their Gear Score.
Skills
Skills have a particular progression order. Each time you level up, you can purchase or improve a specific skill with coins. You can also skip to other skills in the progression by spending gems. Active skills will map to a button in the lower-right corner of the screen. Passive skills will either be always active or activate automatically when certain conditions are met.
Spirits
Inserting Spirits (or Runes) will also improve your weapons and armor. They are are diamond or triangle-shaped items that will convey extra elemental bonuses. To add a Spirit, you first need spend gems to drill a socket in the item to be improved.