Originally Posted by Seil
There are a decent number of items bought with coins, like potions and lottery boxes. But I don't think any of them are necessary. And judging from the previous discussion, the only monster that requires paying requires you obtain VIP 1, which costs $2(10 coins, 9 coins is $0.99). You don't spend the coins, you just have to have purchased that many to unlock VIP.
So I'm under the assumption that any items required to obtain certain monsters can be obtained freely, as well. But this is just me assuming, I'm not far enough to know for sure.
Well since I'm quite far into the game I can tell you how it is
The item you see in the shop, they are also all obtainable in the game without paying a dime. After you complete a stage, there is a spinning reel with rewards that you can get, from there you can basically get almost everything, from chests to revive potions that costs gold in the shop. Because the fact that you can do those maps as MUCH as you want to, you can get plenty of the items if you put in time and effort, but there is also a luck element into what appears on the reel aswell as what you land on. Like a roulette. buying with gold is more for the rich and lazy.
Note: Things you get from chests are things that you CAN also obtain by just playing and grinding normally. The rewards are not things that only you can get by paying.
I think all in all there is 2 items that you can't get without buying with gold coins, a revive card if you dies during the map and a cheat dice that you can select number with. Tho you still get these items, 1 from daily reward everyday and the other one from lvling up, doing quests etc.
Edit: Almost forgot, during certain maps there are treasure chests on the map, if you land on them you can get anything thats in the gold shop, such as chests, potions etc.
Hope that clears it up.