Upgrading of weapons
I merge low level and other weapons with my 3 star weapons to up the level of the 3 star weapons then with the higher level weapons I merge them with the weapons I want to level up. This trick seems to save me money.
There are daily quest to complete and there are two bounty that drops familiar summoning and refining material. I recommend to do these two. Do what quest you can do as they usually have reward like additional energy, money or exp. Some of the quests I think are not worth doing since they are way too difficult like, finish 13-1 without getting hit once.
Also do the events as they require very little energy to get a considerable amount of exp and also rewards.
If you have a little money u can also spend on the monthly crystal mpass which cost around 7 dollars a month. By buying crystals also adds to your bonus meter. Also there are strategies in this game.
Other world farming
farm for crystals to buy the other world gun to fuse with my current fs to make my weapon into a 6 star. Then I started farming first for the other world weapon to merge together for the 6 star weapon. It seems that you do not need to reach level 99 to go from 5 star to 6 star. Then I farmed for the crit damage and speed up badge which cost 5000 crystals. I got 3 of them. But I think you only need 2 as you need something to boost your total hp. Something with the braveheart skill or similar. Then there is also the +10 skill level badge/weapon/uniform which cost you 2000 crystals
Now playing gunz girl on my iphone. I am still figuring out the quest below ?? cost to complete 13-1. I have quite a few quest which I am unable to see the full details of the quest as rewards seem to be blocking the details.
Different bosses require different fighting tactic and also. Sometimes i believe the recommended level is a lie. There are some in which you can win there are some which are level 130 or so but you still can’t beat at level 230+ I guess equipment maybe plays a big part.