A couple of ideas inspired by the recent Seven Vaults-A-Leaping.
- Make it permanent. A new four star in the vault every day would be awesome and would encourage additional spending (of HP anyway). Increased frequency could make it possible for people to get that exact four star cover that they were missing. With 41, available four stars (not including Howard & Devil), each color cover would only come up every 123 days.
- Align the four star vault such that the vault contains the required four star on the crash of the titans day. Again, this encourages people to spend HP (and hopefully cash) in an attempt to beat crash of the titans.
- If you’re unwilling to do a new daily four star vault, do a hybrid and simply change the frequency to five days, aligned with the crash of the titans event (again, encouraging people to get covers to beat crash of the titans)