IAP guide

[spoilerspree]

Best buy -

Field Sphere (let you obtain other IAP stuff faster than grinding divine shard)
Use Sphere
Forgotten Key
Money Sphere

Optional -

Maid Coin Sphere*
Treasure Key (contrary to game said you need 9)
Weapon Sphere
Eclipse Shuriken, Enma Card (make Madam Curie much easier and require less stat grinding)

Notable thing you can obtain from other method -

Hunting Garb from arena coins
Bathing Apparel and Happy Jacket from farming (start with ele dmg boost armor from arena)
Barrel buster for Magatama and effect stone (everything there are "farm"-able)

The other item arent worth it. Yes it includes the usual "attract" equipment Step by step Clog. Dungeon mobs are summonable while overworld mobs arent that good.

*Maid Coin Sphere atmost only useful to reach enough stat to beat lvl 550 secret battle arena with ease. The reward is 10 Ultimate Jugs and 5 Exquisite Jugs. This is faster than buying single stat jugs with maid coin.