The characters in 7Balls NFT have various Five elements (Metal, Wood, Water, Fire, Earth) with different class (Attacker, Tanker, Slicker, Supporter), and assorted levels of D,B,C,A,S,SS,SSS.

Five Elements:
Metal carved Wood, Wood carved Earth, Earth carved Water, Water carved Fire, Fire carved Metal. For instance, in Fire carved Metal, characters in Fire will have the hit with more damage into the characters of Metal and conversely the characters in Metal will have the less damaged hit as fighting into the characters of Fire.

Attacker: power in attack, critical damage, low resistance
Tanker: power in resistance, high HP, low damage
Slicker: power in control effect, sucking blood, buff to increase the attacking power for the whole team, attack and resist in balance
Supporter: power in blood recovery for the whole team, creating shield to protect, armor buff, reducing critical damageā€¦ with medium resistance and medium attack
Levels of Heroes: D,C,B,A,S,SS,SSS. The higher level, the rare it is. Update your hero to upgrade the power
Possibly burning Heroes in the lowest level to receive items and upgrade skills.