I got the idea from the 4th event objective's description (beat area 200 while supplies last).

How about an objective in a campaign where we start with X gold (has to be quite generous though) and we don't gain any gold from killing enemies/opening chests? The objective could be something like "clear area X using only the X gold provided", making it quite a challenge since we have to figure out which crusaders to level for their abilities. It's tricky since it shouldn't be a cakewalk nor nearly impossible, even for more experienced players with 10k idols.

I guess more experienced players will know (roughly) who to place and level up.,.but yeah, it could be a trial and error objective. Knowing how things work though, there will be a forum post a couple hours later with an "ideal" formation or how far X gold will take X crusaders. EXP points will help with progress if someone gets stuck near the end.

To be honest I'm not a big fan of the idea (even if I was the one suggesting it, hehe), but I like a bit of a challenge every now and then and I've met that kind of objective in other games. Just thought I'd leave my suggestion here and see what the rest think of it.