On Paper, Melissa seems completely broken or overpowered but in application, she is very lack luster.
With the current meta, Melissa, being a unit designed for PvP, she lacks a lot of things, one of them is that, she sets up the team but insteadsshe needed the team to set her up, another is that, she can't make use of her Curse debuff as a pure damager as she will be lacking the Effectiveness stats that she would need to proc the Curse, and as a damager that relies on Curse, she will be lacking the damage to kill.
This kind of makes her, a pretty bad unit, knowing that, she needs a whole team to make her work.
Now, This suggestion is merely a suggestion, it may be good, it may be bad, but eitherway, this will be according to her Lore.
Skill 3: Blood Bloom
Dispel's debuff before applying Curse.
Curse now applies to bosses but the damage redirect is halved.
The reasoning for this is the PvP meta, it's either a lot of them has Immunity Sets despite being a damager, which renders Melissa's curse, useless, as for the boss applicability, this is so she isn't as useless PvE wise.
Skill 2: Changed into Passive: Vampire Lineage
Increase Attack, Speed depending on lost HP.
Grant Immortality when taking lethal damage (8 turn Cooldown).
When a Cursed debuffed enemy dies from Curse or Melissa managed to kill the target with her skill "Blood Bloom", Melissa Gain's the buff "Vampire Lord".
When "Vampire Lord" buff ends, apply the debuff "Hunger" to Melissa.
Cannot be Stolen and Dispelled.
Grants increased Damage by 25% and decreased damage recieved by 25%.
Changes her Skill 3 into Manifestation.
Unit takes 25% of Max Health per turn.
Increase Effectiveness Resistance by 50%.
Lasts for 3 turns.
Cannot be cleansed.
Unit cannot be buffed.
Cannot be extended.
Deals 50% less damage and takes 50% more damage.
Healing effects are halved.
Combat Readiness boosts are halved.
Effectiveness Resistance are set to 0%
Lasts for 3 turns
Dispel this buff if the unit kills a unit.
Lore wise, for those who have readed it, Melissa is a strong unit, being able to out power Haste and Pyllis and even outrun Assassin Coli and Assassin Cidd which have top tier base speed, if she wasn't hungry and starved, she can easily kill all 4, it is sad that espite her lore, her skill is lacking, both is practical and general.
Given that, if She can steal Haste's strength, we know lore-wise that she will become a very powerful Vampire Lord, even able to revive the dead.
Vampire Lord Buff S3 skill: Manifestation
Immortality is removed.
If the skill managed to kill the target, Reset CD of this skill.
Grants Melissa a buff called "Blood Bank" whenever this skill kills a unit that stacks up to 3 times.
Cannot be dispelled
Decreases the duration of Hunger per stack.
Heals Health depending on the number of stacks:
1 stack, Melissa Heals 20% of Max Health when the debuff "Hunger" is applied and decreases the duration of the debuff by 1 turn.
2 stacks, Halves the egative effect of the debuff "Hunger" and Heals 30% of Max Health and decreasesthe duration of the debuff by 2 turn.
3 stacks, Melissa Heals 50% of Max Health and cleanses the debuff "Hunger"
Skill 1: Might
When Melissa has the buff "Vampire Lord", increase Combat Readiness by 10%, and another 10% if the Unhealable debuff is applied, when inflicting critical damage, decreases Cooldown of "Manifestation" by 1
Soulburn: removed from "Might" and moved into "Blood Bloom" and "Manifestation" when Melissa has the Vampire Lord buff on her
Blood Bloom: 20 souls, Ignore Resistance
Manifestation: 20 souls, Increased Damage
This are mere suggestion, that I think will fit Melissa's gameplay and lore together as one.