Don't spend money on buying new equips.
Don't spend money on upgrading equips, better to save them for enchanting units to +5 for combining.
Start upgrading equipment at level 25+ that is when the game becomes challenging.
Always equip your monsters with latest weapons and armor, even if it's white. Better than nothing.
Level up units that are not "Mastered" yet to get free cash points!
If you aren't going to combine mastered units, feed it as fodder.
You can earn rank A and S monsters as monster drops later on, so focus on leveling.
If you need to earn gold, you can do so at the endless dungeon located on bottom right of world map.
If you want, you can save your Free Cash gems for awesome outfits in Cash Page.
Make sure you add random friends and accept randoms, can't go wrong just press buttons.
Don't worry about power leveling all your units evenly, you can easily power level at the last stage or hell mode.
You get a free Rank S character at level 30!
Don't ever buy weapon gacha with real money because you can obtain epic gear from raids.
Mastering units become a lot easier around level 30, takes about 4-5 runs.
I just beat the final boss, added the crazy epic gameplay video. You also get 200 cash gem after you beat the game! You will unlock a harder nightmare dungeons, then after that hell mode @_@!! Perhaps a new ending after beating nightmare mode? The last boss fight was crazy watch out for spoilers!