Charles Dunn

— PROJECT NAME

Hearthstone Mercenaries


— ROLE

Contract Game Designer


— Publisher

Blizzard Entertainment

My design role on Hearthstone's Mercenaries game mode focuses on design and implemention, including new boss fights and Mercenary characters. I've also been significantly involved in determining balance changes and design direction for the mode's content as a whole.


Prior to Mercenaries' release, my primary role was playtesting the mode's in-development PVE and PVP content. I gave feedback on player progression, difficulty, and balance tuning. I also identified, reported, and fixed design bugs.


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Mercenaries Mode

Hearthstone Mercenaries is a game mode within Hearthstone, a character collector RPG with rogue-like elements.

Players collect unique Mercenary character cards (called Mercs), level up their stats and abilities, create teams of 6 Mercs, and use them to complete PVE bounties, or compete against other players in the Fighting Pit.

Game Balance Testing

Mercenaries is a very progression focused game mode. My initial role involved testing the core PVE systems, to simulate a wide variety of player types and behaviors. I would test progression emulating free-to-play players, hard-core players, casual players, and everything in between.


I worked closely with designers to ensure that the progression and balance of the game felt fun, engaging, and satisfying for all types of players.

Boss Design

After the progression systems were finalized and the game mode was publicly released, I transitioned to a content design role to design and develop post-launch content. I designed, implemented, and balanced new boss fights and Mercenary characters.


When setting out to design boss encounters, I prioritized encounter mechanics that would highlight specific Mercenaries, giving those specific characters (and party compositions built around them) the chance to shine through their unique abilities.


For example, the Vaelastrasz boss fight does a crushing amount of damage to the player’s characters, but also gives them powerful buffs to help overcome it. This encouraged players to use burst damage Caster characters like Bru’kan to best utilize the double damage buff.


Merc Design

My current focus on Mercenaries is the design of new Merc characters. I really love doing this type of character design work, by creating new and interesting abilities, and delivering on cool themes for our players.


When designing and balancing new Mercs, I balanced the dual priorities of ensuring they were balanced for the PVP environment, but also create interesting and unique abilities that we could highlight in PVE boss designs.


For example, Sky Admiral Rogers' Master Tactician has the unique ability to force a character to act next, out of the normal speed order. This has proven very versatile in PVP, but also has opportunities to shine on boss fights like Vaelastrasz, in order to allow your slower character to preempt the boss’s Sweep Aside ability.

Mercenary Character Design Process

Step 1

Background research on the character


Understand the themes we are trying to hit for the character, how we have portrayed that theme already in Hearthstone and other games.


Yrel is a fanatical devotee of the Holy Light. This aggressive, zealous theme is the core of her Mercenary identity.

Step 2

Understand the current state of the Mercenaries roster


How does this character fit into the current game? What teams does this character want to play with?


Holy characters in Mercenaries fall into two main categories: attacking Paladins (like Cariel, Cornelius, and Tirion) and Holy casters (like Anduin, Velen, and Uther).

STEP 3

Identify overlaps from steps 1 and 2


There was a definite lack of Fighter Mercs (green icons from step 2) in the current Holy team, and considering Yrel’s aggression, it felt felt appropriate to make her a Fighter.


Yrel is intended to be played with mostly (or exsluviely) other Holy characters, due to her fanaticism and the abundance of Holy options.


STEP 4


Create initial designs of abilities and equipment that follow from step 3, such as the four shown below. Zoom in on each ability for more details.


Raidant Light plays well with other Holy characters who care about stats.

Hammer of the Naaru plays well into the Attacking Paladins build.

Wrath of the Lightbound is a powerful effect! But it can backfire if you have non-Holy characters on your team.

Libram of Wisdom is a big payoff for the Holy Caster team, which cares about Holy Damage and Healing Power.

Step 5

Implement, test, and interate


I implement and script all of the abilities and equipment using Hearthstone's proprietary tools.


Then, we open the character up to testing by other designers, as well as the wider Hearthstone team.


I collect feedback on how interesting the abilities are, how much fun they are to use, and how well they are balanced. I use this feedback to iterate on the initial designs over the course of several weeks to reach the final design shown here.


Boss Design Process

Step 1

Background research on the character


Much like designing a Merc, designing a boss starts with understanding who this boss is, what makes them a compelling enemy, and what themes or signature abilities are important.



Vaelastrasz’s defining ability is “Essence of the Red” which provides a huge buff to the player, but they are going to need it overcome the immense challenge of the boss fight!

Step 2

Identify Mercenaries that we want to highlight



To design a good challenge, you need to understand what tools the players will have to overcome it.



Each boss will typically consider a Merc that is released in the same patch, and look to highlight one or more of their abilities or effects.



Vaelastrasz grants Windfury with “Essence of the Red”, and himself is a Protector. Which makes him particuarly vulnerable to Casters that can use a physical attack, like Sky Admiral Rogers.

Step 3

Design abilities and mechanics based on steps 1 and 2


Above is the final paper design for Vaealstrasz.


I prioritize reusing existing abilities and effects (highlighted in orange) wherever it makes sense in boss designs, to avoid cognitive overload on the player, and to maintain clarity.


The only new abilities that I introduce in a boss fight should be the ones that are the core mechanics and thematic for the boss.

Step 4

Implement, test, and iterate


Like Merc characters, I implement and script bosses using proprietary Hearthstone tools. This implementation includes ability functionality, voice over and artwork hookups, and enemy AI behavior in Unity3D.


The boss is playtested by other designers who use a wide variety of team compositions to thoroughly test its many interactions. I make design iterations and balance tuning adjustments based on this feedback.