1 Rainbow Gem will be received upon every difficulty first clear
Weekends (Saturday and Sunday) Limited Event
Weekends (Saturday and Sunday) Island provides a large amount of Beli
EXP gain: Golden Cave: 68, Golden Cave (I): 1240 or 3275 (the latter if you encounter rare boss Fullbody)
Beli gain: Golden Cave: 25-55k, Golden Cave (I): 45-105k
Different units drop bags of different values, through each one will also generate 200 beli per kill. There are some alternative stages, and it is possible to see, for example, no lobsters at all during the run.
For GC, roughly, the value of bags is as follow: regular grunts,1,5k, lobsters, 5-8k, ,boss Higuma - 25k.
For GC(I), roughly: Boss drops a bag worth 30k, sub-boss Fulbody and lobsters, 15k and evolved "big" marines,7.5k, regular grunts, 2-3k. It is possible if unlikely for a stage to drop no bags at all. Depending on whether you can collect valuable bags or not, your beli will vary significantly. Always target the units which drop high value bags first to try to trigger their drop first!