- All x2 HP\Attack God cards - Demeter, Agni, Poseidon, Angel, Persephone (Both 5* and 6*) (Did someone see them recently?)
All -50% damage Human cards - Catalina, Necromancer, Achilles, Blackbeard, Dragon Knight.
All 6*+ Demon cards - Reaper, Lilith, Cyclops, Demon, Gabriel.
All 6*+ Recovery cards - Phoenix, Dryad, Mermaid Princess, Unicorn, Homunculus
Let me present list on cards you should buy from shop.
This list intended for new players, so high level players won't benefit from it.
1. First card you should search in shop is healer.
Main goal is to get 6* water or light healer, so buying 4* to evolve also viable option. (You can get both 4* healers from Chapter 5)
After (or if) you have healer card - go to next step.
2. HP cards.
This will be your main hunting goals for long time, because you need all five colors and 7* evolution of them.
So always have 2kk gold in pocket for one of this beautiful cards. Snake Spirit are best of them due to value of poison. Naga are better in GW.
Now we finished with absolutely necessary cards and come to territory of "good to have" items.
3. Rainbow Pirate Treasure Map
Always buy it when you see it in shop. Required to evolution of 6* and higher cards, so later you will need tons of this materials. And chances to get it are very-very low. For example after 10 runs of Void Fields I still don't receive it)
Also you can consider about buying all Rainbow items (except coins). They are not so common as drop, so it's good to have 3-5 of each in stock.
4. 2x HP\Attack
That's the only 2x HP\Attack cards you can buy from shop - and they will help your mono color team.
5. 50% damage reduction
5* Master Fencer
5* Musketeer
5* Fallen
That's only -50% damage cards you can buy from shop - so grab them! They allow to survive mono color levels with heavy damage, like Insane Panzer or Raid Bosses.
6. Zeus
Mighty Zeus, that will speed up killing of high HP bosses - Panzers and high level RB.
7. Different good cards:
Very good at start, loosing her value after you get two HP cards.
Nice poison damage at 7*
8. Energy Potion x2, Revive Potion x2
This you will buy on spare gold before end of week, to spend in Solomon Mines and get more gold ... that you will spend on potions that you will spend in Mines and get gold to buy potions ...
9. Golden and Purple Treasure Maps.
Same as with rainbow - they are hard to get, and you need many of them in most of evolutions. So it's good idea to buy from shop, if you are low level.
After you have 100+ energy it's better to get them from Void Fields.
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In general you can buy all cards from shop if you have enough funds to to so.
But in case of limited gold supply - feel free to use this list as some kind of reference on how spend your money in best way.
And last reminder - this list is for starting players, not high level players)