In the Boss raid, you can do it solo or with a party. Talk to the agent cat at the left side to solo or the opposite side for party. You won't lose any exp if you die in there.
I always died at Jr. Balrog.
As for Secret Agent event, I don't have much luck using Chaos Scrolls.
My permanent Glove and Hat are ruined.
The glove starts with HP +30, WA +3, 4 slots clean, ended up with HP +15.
The hat starts with All stats +3, HP +10 6 slots clean, ended up with the DEX stats missing.
I wished that I just use normal scrolls.
Also, as for the Secret Box, you can also get that by completing the 'Today's Mission' Quest.
I always died at Jr. Balrog.
As for Secret Agent event, I don't have much luck using Chaos Scrolls.
My permanent Glove and Hat are ruined.
The glove starts with HP +30, WA +3, 4 slots clean, ended up with HP +15.
The hat starts with All stats +3, HP +10 6 slots clean, ended up with the DEX stats missing.
I wished that I just use normal scrolls.
Also, as for the Secret Box, you can also get that by completing the 'Today's Mission' Quest.