Acknowledging that this is not a bug and clearly working as intended, but the intent is faulty.
Suggestion: Remove the ‘Claim a Sigil’ challenge from Darkmoon Faire and any other events.
Reason: The inclusion of this challenge encourages a non-participation playstyle. In order to complete the challenge, at least one available sigil must be attainable with the leaders/troops at the player’s disposal. If a player has progressed naturally through the campaign zones, they will inevitably reach a point where they have either obtained all sigils or are unable to continue until their troops gain significantly more power. With the upper-tier sigils being locked behind level 26+ missions, the resource cost required to transition an army from “Can not win” to “Can win” is substantial. Consideration should also be taken for minis that have not chosen the “best” talents first, requiring an Epic upgrade to unlock basic utility, furthering the resource cost for a viable army.
There are obvious workarounds to this dilemma. I’m sure the corporate-preferred solution is to complete as many micro-tran$actions as it takes until everything is achievable. A more frugal and available approach is to simply stop progressing in the campaign missions. By not participating in the content, it will be later available to satisfy the requirements of challenges such as these. Since fear-of-missing-out (FOMO) seems to be a driving force in online/mobile development, it is important to recognize how this phenomenon may persuade users to avoid interacting with your product. All of those missions I could have completed are still available, and this challenge will never be challenging, nothing is missed. Those who have already challenged themselves to the limit and are unable to progress will likely not change that prospect within seven days.
In conclusion, Participate FOMO, non-participate no FOMO.