Any guides for upgrading cards?

[Perse]

I have been stashing boat loads of extra cards, prisms, sub-att changers and the like. I want to upgrade some of my cards but I don't want to mess up the good ones I currently have. Any advice?

[TobinPowellHeath]

Use prisms, because there is no risk, and the percentage is already low. Just try to use them on already good cards, in case they actually work.

[yiyagiteller]

i tried using legend pro cards to upgrade, after wasting about 3 of them i never tried again. (i also tried rookie legends, fusion legend card but these do not yield higher % either. also lack of cards so just whatever i have)
i used normal and magic cards to upgrade and a lot of points, i'd guess somewhere around 300k to 400k to fully upgrade one card. never did them in one sitting and spent 100k at a time. yesterday i spent 84k to get a card from 6/8 to 8/8. luck is involved as all things fs2.

[momo24]

I have tried to upgrade cards for 10 of characters (mine and my friend's).
My experience is you need at least 200k to upgrade 1 set sp card. In most case, you will need 30k-40k.
First, use rare cards for +7 to +10 (you will need to success like 6-7 times). There is a certain point that you will keep failing, I think in most case from +9 to +10 is the hardest, and each trial will waste like 35 upgrade spray. In this case, try to upgrade those you never did (+7 to +8). If you keep failing from +8 to +9, you can try to upgrade those +9 to +10. You have a higher chance to upgrade your +9 to +10 (and the failure from +1 to +2 is like 6 spray or 12 spray, very small amount).
Once you reach +10, you have like 2 or 3 tries to get to +12. You will need to use pro cards, it gives certain boost of the success rate. I have tried use rare cards, it has lower chance, and waste a lot of points. And do not force it if you fail more than 3times. It will cost you like 100 spray which can make your other card from +7 to +9/10. Try it another day. If you feel lucky today, you can try to keep upgrading the card until you begin to fail.

[9cm]

Basically as what momo says, try to upgrade your cards to +10 first. In the +10 to +12 will cost a lot of sprays. While you keep failing, try to upgrade other cards. Then tried back +10 to +11 again.
In this game, if you keep upgrading 1 single card, you will spend over 200k. But you can use 100k of those 200k to upgrade other cards. It's a management theory. How to improve your efficiency of using those sprays.
While you reach +10, what you need is luck, and yes pro/legend cards work better in this stage.

[Zydrunas]

The higher the rarity of the fodder card, the easier it is to upgrade. HOWEVER, the likelihood of upgrading a card to full stars is highly unlikely, so it may not be worth using legend cards for the last two upgrades.

For sub-attribute changers, the technique is to keep duplicates of the cards you want to equip. Sub-attribute change one card until it is acceptable, then sub change the other until it is better than your other one and repeat. This is so you have a fall-back option and so you don't lose progress.

[Junior]

The higher the rarity of the fodder card, the easier it is to upgrade. HOWEVER, the likelihood of upgrading a card to full stars is highly unlikely, so it may not be worth using legend cards for the last two upgrades.

For sub-attribute changers, the technique is to keep duplicates of the cards you want to equip. Sub-attribute change one card until it is acceptable, then sub change the other until it is better than your other one and repeat. This is so you have a fall-back option and so you don't lose progress.

i did this he is correct

[KobeBlaise]

The higher the rarity of the fodder card, the easier it is to upgrade. HOWEVER, the likelihood of upgrading a card to full stars is highly unlikely, so it may not be worth using legend cards for the last two upgrades.

For sub-attribute changers, the technique is to keep duplicates of the cards you want to equip. Sub-attribute change one card until it is acceptable, then sub change the other until it is better than your other one and repeat. This is so you have a fall-back option and so you don't lose progress.

+1 best answer, could not explain any more perfect than that.

[Perse]

Thanks for all of the replies. I still haven't started the upgrades yet but your advice is awesome. <3 Buck