All planes are purchased, ranked and leveled up like this:
- planes (except Sparrow) must be purchased for credits or crystals
- planes (except Laserbite) becomes available for purchase after a certain level is completed
- planes go for a 40 % sale every once in a while, but the sale is only for crystals
- initial level of plane is always 1
- max level is 140 (currently at least)
- you level up by paying credits. At first small amounts, but then larger and larger amounts.
- you can also level up for crystals
- the planes also have a rank C (lowest), B, A, S and SS (currently highest)
- the planes have different initial rank (but always initial level 1)
- you will collect plane cards to evolve the rank of the plane
- rank C has top level 40, B top level 60, A top level 80, S top level 100, and SS top level 140
- you can raise the rank, without having reached top level of previous rank. (This should mean that you can have a rank SS plane of level 1.)
- rank C to B requires 80 cards, and then 100 crystals
- rank B to A requires 160 cards, and then 200 crystals
- rank A to S requires 240 cards, and then 300 crystals
- rank S to SS requires 320 cards, and a whopping 800 crystals
Evolvement of rank is often a great increase in armor, power, overdrive and also perks. Each level increase is of lesser significance. We recommend that you rank up your favorite planes as soon as you can, but that you level up sparingly. Except for ranking up from S to SS: that is just luxury considering the cost.
We also recommend that you never use crystals to increase the level of the plane. Save the crystals for things not possible to purchase with crystals, like ranking up.
It is in most situations better strategy to level up and rank up several planes, rather than just go for one or two: This will make it easier to win the entire assault. You will be able to pass all 30 bosses in assault if you develop 6 planes in parallell, rather than maxing one plane at the time. And assault is the main key to gain more crystals.
Finally: Consider better your devices instead of blindly level up your planes. Getting better devices will affect all your planes.