Chenyang Huang
© Chenyang Huang

LIMITED-TIME EVENT

Valhalla: The game uses a risk/reward system where taking on tougher conditions leads to better rewards.

Vision

There are usually two types of limited-time events—one for player engagement, the other for monetization. Of course, engagement events can still drive revenue, just more indirectly.


In this case, the goal was to boost long-term retention and engagement, especially since idle games tend to get repetitive over time. We noticed from the data that when player progression slows down, session length drops significantly—and that eventually hurts revenue too.


So I designed an event system that doesn’t change the core combat, but completely shifts the strategy and pacing. My inspiration came from Arknights’ “Contingency Contract,” a popular system in Asia that consistently boosts session length.

Core Mechanic: Player-Chosen Difficulty

The core idea is: the higher the difficulty, the better the rewards. But it’s not just choosing “Easy / Hard.” Players customize the challenge by selecting from different modifiers:

  2. Enemy Buffs – more HP, more enemies, extra passives, boss fights
  3. Self-Nerfs – lower stats or restricted skills
  4. Restrictions – team size limits, faction-only teams
  5. Hard Combos – pre-set extreme combinations by the system


To keep progression going, I also added a simple mastery system—a small trick to allow light stat growth during the event, so F2P players don’t hit a wall too quickly.





Core Mechanic: Player-Chosen Difficulty

The core idea is: the higher the difficulty, the better the rewards. But it’s not just choosing “Easy / Hard.” Players customize the challenge by selecting from different modifiers:

  2. Enemy Buffs – more HP, more enemies, extra passives, boss fights
  3. Self-Nerfs – lower stats or restricted skills
  4. Restrictions – team size limits, faction-only teams
  5. Hard Combos – pre-set extreme combinations by the system


Mastery System


To help players gradually grow stronger during the event, I added a simple mastery system. It’s a small trick—but important. In F2P games, player progression is much slower than in single-player titles, so without some kind of scaling, most players would quickly hit their power ceiling and lose motivation.




Results & Considerations


After the event launched, player session time almost doubled. What made it so engaging was that players could experiment with different combinations based on their team setup, pushing for higher rewards. That strong sense of progression and customization really drove engagement.


The downside, though, was that because players could attempt it as many times as they wanted, some started to burn out. It clashed with the game’s otherwise casual pacing.


So we had to add some constraints— tickets—to limit the number of daily runs and avoid player fatigue.




Wireframe

QA Test plan

Playtest & Themetry

The key to this event is ensuring that the difficulty smoothly increases over time, so we conducted a series of internal tests to ensure players have a good experience.We will also collect player data after the event to verify if it aligns with our design approach, allowing us to make adjustments for the next event.


We pull out some player data from the server and separate them into four groups based on their level to ensure all groups of players have a good experience.