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There are 5 different characters in Zawia RPG. Characters gain levels as you win battles and character levels are permanent between plays. Characters gain stat bonuses and new skills at levels 5, 15 and 25.

Your character gains 1 skill bar per round during battle, up to a max of 6. The L5 skill always takes 2 points, the L15 skill takes 4 points and the L25 skill takes 6 points.

Characters

AP Character
Bonus
Skill
Level 5
+5% AP
+50% damage on the next attack
Level 15
+10% AP
+50% damage on the next 3 attacks
Level 25
+15% AP
For the remainder of the battle, adds a shadow clone which attacks every round for 50%

The shadow clone will crit/combo when you do and benefits from the L5/L15 skills.

HP Character
Bonus
Skill
Level 5
+8% HP
Heals for 10% before your next attack
Level 15
+16% HP
Deal 400% damage as the next attack (cannot crit/combo)
Level 25
+24% AP
Poisons the enemy for 3 rounds, dealing 6% of enemy HP per turn.

DP Character
Bonus
Skill
Level 5
+5% DP
Reduces the damage you take next round by 40% (or 20% for energy damage)
Level 15
+10% DP
Deal extra counterattack damage for the next 3 rounds which scales with defense instead of attack
Level 25
+15% DP
For the remainder of the battle, you have a 20% chance to reduce incoming damage to 0 (and double the counterattack damage that round)

I'm not entirely sure how the L15 damage is calculated. It says "150% of defense" or E-Shield. In my experience it tends to be deal about the same damage as my attacks.

Combo Character
Bonus
Skill
Level 5
+5% Combo chance
Guarantees a crit next round based on 90% AP (180% total damage)
Level 15
+10% Combo chance
Deal 10% of the enemy's current life and heal for that amount
Level 25
+15% Combo chance
Instantly kill a single non-boss enemy. Has a 3-battle cooldown.

I haven't found a way to make this character useful on Ultra Mode but on normal mode the high healing capacity and insta-kill could theoretically be useful.

Crit Character
Bonus
Skill
Level 5
+5% Crit chance
Adds 50% dodge chance to the next attack (33% for energy attacks)
Level 15
+10% Crit chance
Add your drop-chance multiplier to your next attack.
Level 25
+15% Crit chance
Increase your drop rate, gold bonus and shard bonus by 15% each.

Your L15 adds the current drop multiplier (starting at 1X, rounded down for a total of 2x damage). You gain +1X chance every 90,000 luck, maxing out at +4X at 360,000 LUC. Pandora's box adds +60% which brings the total multiplier to 8X. The L15 brings it up to 9X. You can reach 12x damage with the "+4% drop" zone bonus. This is a great character for farming with max luck.