Event mode is one of my favorite things to crash through. I'm pretty new, but I can get through most of the challenges... And on fillia and big band, the RNG gods have graced me with characters strong enough to beat the "only with X" challenges. That being said... I think they could have a bit more in terms of rewards. My initial thought is a character relic (for that event, of course) for clearing a boss. That might be a bit too much of a reward, however... So maybe a point system? Every 100% clear (for easy, advanced and expert modes) gives a point or token, and 5 or so would give a free character relic. The way story mode gives out character relics works, and I think event mode should emulate that just a bit: give a tiny chance for a gold by continuing to beat challenges each week, even if it takes a few weeks to get the relic.