When you start out, you will be given a choice of one of 3 cards and deck of corresponding faction. The choice isn’t that important here, you will be able to get all unevolved 1-star cards you need easy enough to change your main faction. 2 3-star cards you get will be unavailable until later, but they aren’t that powerful anyway. But if you are after a bit of extra usefulness, I would advise you to get Sakari of the Ninja Unit and Cyber faction deck, as Sakari can be quite good with her 25% dodge chance.

Do NOT open any card packs you get early in the game!

The reason for that is that the first time you offer a card pack, you will be given a free Card Selector, an item that allows you to pick any card from the pack, which will have to be used on the card pack you open as a part of tutorial. If you use it on one of 1-star packs you will get early it will be completely wasted.

Instead, keep playing through scenario until you have accumulated 25000 Gold (it shouldn’t be too hard with your starting deck), buy Female Transformation Card Pack and open it. This will allow you to pick a powerful Super-Evolved 5-star card (I would personally advise you to get Youkai: Tengu Girl S, who has very high attack, ability to act immediately after summoning and cost-reduction if you have other Spirit in play).

For certain in-game achievements, you will be given a choice of one of 3 cards, in case of 1-star to 3-star cards the choice isn’t that important, as these cards will be more or less easily available later anyway, but in case of several 4-star and 5-star cards the choice is very important, particularly since cards offered there are hard to get otherwise.

These achievements offer you the choice of 3 Domain Interrogators Shadow Trinity. Between them, you should ALWAYS pick Kells one! She is not only the best of the 3 and the only one who is actually useful in the long run, but also a very important card for beating end-game opponents due to her skill, that destroys all opponent’s cards.

As a reward for this achievement I would advise you to choose Tiamat. She has top-notch defense, absorbing attacks from wide variety of attributes, negating damage from 1 and 2-star cards and having high HP for the attacks that can hit her. And she is quite good at offense too, with both decent base attack and ability to deal double damage against Spirit card (who are quite common). Her only disadvantage is the she also has wide variety of types, increasing the chance of running into someone who resists or absorbs damage from one of her types.

Now this is a hard choice: you can get a super-evolved version of Tiamat, who is even stronger than the evolved one (with quadruple damage against Spirit cards!), or Dimension Administrator Bahamut, who is much less useful in battle, but an excellent commander if you use Spirit-centered deck.

Important thing to remember here is that you will need a 2nd copy of Bahamut before you can use her as a commander, which you will only be able to obtain in PvP. And while extra Capture Rings can be hard to obtain, Tiamat will likely help you more towards obtaining extra Capture Rings than Bahamut, and even if you don’t find someone to get extra Tiamat or Bahamut from, even 1 super-evolved Tiamat can be a powerful asset.

So I would personally advise you to pick Tiamat, though Bahamut can be worth considering, depending on circumstances (for example, if you have a basis for a good Spirit deck, and know someone willing to let you get 2nd Bahamut off them).

As a reward for this achievement I would advise you to choose Magical Girl Hizumi. She is not that good in endgame, but she can be a valuable card in early to mid-game, as Humans are quite common and having one on the battlefield allows you to summon her for just 2 mana.

You can easily get powerful free cards for achievements of evolving and super-evolving a card in battle up to 500 times. For 250 times, you can get Domain Interrogators Shadow Trinity (Kells), and for 500 times you can get Tiamat or Bahamut (read above for more details about them).
To get these powerful cards easier, I would advise you to build early decks with exact purpose of allowing you to evolve a card maximum amount of time in a single battle: first make a deck of 5 4-card sets of unevolved cards, and once you get 500 evolution achievement and can afford it, a deck made of 5 -card sets of evolved cards.

Even if you lose a battle, you don’t lose anything, only gain a little extra gold and experience, so don’t be afraid to lose scenario battle and focus on getting these achievements early.

When you win a ranking PvP, you are given a choice of 10 cards from opponent’s deck, and can capture one of them if you have Capture Ring.

NOTE: your opponent doesn’t actually lose the card you capture; their only penalty for losing is a loss on their PvP record, which may or may not matter to them.

Also IMPORTANT: the first time you win a ranking PvP, you will be given a free Capture Ring, which you will have to use immediately as a part of tutorial. So ideally, your first win should be pre-arranged against an opponent who has a card you want to get, and who will only use 10-card deck to make sure you get the card you want with your free Capture Ring.

This game has 4 DLC, which aside from extra dungeons, let you get extra free cards, some of which can be quite useful early on.

I would say it is the best DLC for starting out, as it gives you evolved and super-evolved versions of Yamato and Kureha, whose skills allow them to attack 3 enemies with full-damage (many cards that have multi-attack skills deal reduced damage to each card), which can be very useful. And even their unevolved versions can be useful early when you don’t have anything better. Super-evolved Yamato in particular has ability that reduces his cost from 7 to 3 if there is a Human on board, which allows you to easily summon him even in early battles where mana is limited.

2nd best DLC to get, as it will give you extra Domain Interrogator Shadow Trinity (Kells), among other things, who will be useful throughout the game (even if can get 4 of them elsewhere, extra 4-star card for levelling never hurts). Other two Domain Interrogators can also be useful in early game, and even Dorothy can be useful when you have nothing better as either battlefield card (she has low HP, but 25% dodge chance if you are willing to gamble on it), or to assist other character (she has high cost, but decent attack for it).

These 2 DLC provide little that boosts your combat performance. While they give 13 and 12 free cards, these cards aren’t particularly useful even early in the game. The only real power boost they give you is that they allow you to collect 100 unique unevolved cards easier, which allows you to get extra Domain Interrogator Shadow Trinity (Kells).

Completing DLC scenarios also unlocks additional store items: both 3-star upgrade cards and 4-star packs divided into unevolved/evolved/super-evolved become available only after you have completed a few of DLC scenarios. Furthermore, buying DLC unlocks extra dungeons associated with these DLC, and some of these dungeons in turn unlock Extra Config options (which make grinding money and experience significantly easier).

So, even if you don’t really want any DLC cards, it may be worth buying DLC for extra store and config options they unlock.

4x Dwarf E (1-cost Spirit, full-power 3-target attack skill)
1x Kureha E (3-cost Spirit, full-power 3-target attack skill, 1.5x damage vs Spirits)
1x Kureha S (7-cost Spirit, full-power 3-target attack skill, 2x damage vs Spirits)
1 – 4x Youkai: Tengu Girl (10-cost / 4-cost if you have a Spirit in play, instant action, powerful attack)
3 – 4x Domain Interrogator Shadow Trinity (Kells) (4-cost, skill that destroys all enemy cards)
1x Tiamat, Lord of Outer Demons E (5-cost, reduced-power all-enemy attack skill, 2x damage vs Spirits, a lot of immunities)
1x Tiamat, Lord of Outer Demons S (10-cost, reduced-power all-enemy attack skill, 4x damage vs Spirits, a lot of immunities)

Strategy:
This is a general-purpose deck that can easily deal with both weaker opponents (thanks to 1-cost Dwarves and ability to summon Tengu Girls cheaply) and stronger opponents (thanks to Domain Interrogators’ skill that destroys all opponent’s cards).
Dwarf’s main purpose is to allow you to summon Tengu Girls cheaper, but Dwarf can also be a valid attacker if you level her to sufficiently high level.
Against stronger enemies, make sure to have Domain Interrogator on board so that you can take out enemy cards. Also, if enemy has powerful cards that Tiamat is immune to, you can use her to draw enemy attacks from Domain Interrogators or yourself: AI doesn’t acknowledge immunities or other card traits when it chooses attack target.
Tiamat’s main purpose is to be a shield for your other cards. Unlike Dwarves and Kureha, Tiamat deals greatly reduced damage with her skill, so only use it against Spirits and when opponent has a lot of low-health cards in play
Further note: if you choose Bahamut over one or both Tiamat, you can make do without Tiamat. Bahamut’s evolved version may also be useful, but I’d say her super-evolved version is too expensive to be useful, except for battles with powerful opponents where mana isn’t an issue.

Further improvements:
1) Add more Tengu Girls as you get them, replacing Kureha.
2) Add 4th Domain Interrogator as soon as you get her.
3) After you have 4 Tengu Girls, use new Card Selectors you get to get Super-evolved Hitomi Kochou, Metamorphosed Human (from 4-star pack). This will lead you to…

4x Youkai: Tengu Girl
4x Domain Interrogator Shadow Trinity (Kells)
3x Hitomi Kochou, Metamorphosed Human S (7-cost, instant action, 1-cost skill that increase another card’s power by 75%)

Strategy:
This deck focuses on killing opponent quickly with very powerful Tengu Girl, boosting her with Hitomi Kochou if necessary. If you can’t kill opponent in a single turn, make sure to summon Domain Interrogator Shadow Trinity to wipe out all or at least most of opponent’s cards, clearing the way for attacking.

If opponent has commander or card that is immune to Tengu Girl’s type, you can use Tengu Girl to assist Hitomi or Domain Interrogator and attack with them instead.