Since ChatGPT came up with the concept of an Angel Mercenary, I asked it to create an Angel Class character and see what it came up with.

Name: Seraphic Avenger

Background:
The Seraphic Avenger is a celestial being sent by the High Heavens to battle the forces of darkness in the world of Diablo 2. This angelic character radiates divine power and wields heavenly might in their quest to cleanse the land from the taint of evil. With their mastery of passive auras, blessings that benefit both themselves and their allies, and formidable combat skills, the Seraphic Avenger is a beacon of hope and righteousness.

Class: Angel

Skill Trees:

Passive Auras:
a. Radiant Aura: Emits a radiant aura that increases the resistance to elemental damage for the Seraphic Avenger and nearby party members. The aura becomes more potent as it levels up, providing increased elemental damage resistance and granting immunity to certain elemental effects at higher levels.

b. Angelic Grace: Enhances the movement speed, attack speed, and casting speed of the Seraphic Avenger and nearby allies within the aura's radius. This aura improves as it progresses, granting higher bonuses to speed and allowing for smoother and swifter combat actions.

c. Divine Shield: Surrounds the Seraphic Avenger and nearby allies with a protective barrier that absorbs a portion of incoming damage. The strength of the shield increases with each level, providing enhanced damage mitigation and improving the duration of the shield.

Blessings:
a. Blessing of Vitality: Bestows a blessing upon the Seraphic Avenger and party members, increasing maximum health and providing passive health regeneration over time. The effect scales with each level, granting greater health benefits and faster regeneration rates.

b. Blessing of Strength: Empowers the Seraphic Avenger and nearby allies with increased physical damage and a chance to deal crushing blows. As the blessing grows stronger, it provides greater damage bonuses and an increased probability of delivering powerful strikes.

c. Blessing of Protection: Grants additional resistance to all types of damage for the Seraphic Avenger and party members. The blessing becomes more potent as it advances, offering higher resistance values and even occasional damage reduction against powerful attacks.

Divine Combat:
a. Celestial Smite: Unleashes a divine smite upon enemies, dealing holy damage and having a chance to stun them. This skill becomes more devastating as it levels up, inflicting increased holy damage and stunning enemies for longer durations.

b. Wings of Fury: Unleashes a flurry of angelic wings that damages and knocks back enemies in a cone-shaped area in front of the Seraphic Avenger. As this ability grows stronger, it inflicts greater damage, increases the knockback effect, and can even temporarily blind affected enemies.

c. Heavenly Retribution: Channels divine energy into a devastating area-of-effect attack, damaging and weakening all enemies within its radius. The power of this skill increases with each level, dealing more damage and reducing the offensive capabilities of affected enemies.

Playstyle:
The Seraphic Avenger excels at supporting their party through passive auras and blessings while delivering righteous justice in combat. With the Passive Auras skill tree, the character provides essential buffs to themselves and nearby allies, increasing resistances, speed, and defensive capabilities. The Blessings skill tree enhances the overall power of the party by granting health regeneration, damage boosts, and damage mitigation. In Divine Combat, the Seraphic Avenger can unleash devastating attacks that deal holy damage, stun enemies, and weaken their foes. This versatile playstyle allows the character to excel both as a protector and a powerful combatant, making them a valuable asset in any group dynamic.

Note:
The above character concept is purely fictional and not part of the official Diablo 2 game.