Max Attack and Defense

To max the stats on a card you use the Arcana Forced ATK, Forced DEF, Forced ATK+ and Forced DEF+. The non + version increase the Attack or Defense stat by 50, while the + version increases the stat by 500. You can use one attack and one defense arcana at the same time for a total of 2 arcana. These arcana can be applied either using fusion or Evolution & Amalgamation.

Since stats are only partially carried over during Evolution & Amalgamation, be sure to apply them only at the final stage of the card.

Maxing Stats cost effectively
Gold cost per arcana is calculated as   when using level 1 N cards as the material cards. For example, a level 6 card would cost  . If the card is at max level, the gold cost is doubled. For example, if upgrading a lvl70 GSR card, the formula becomes  . This means that upgrading a level 70 GSR card will cost more than upgrading a level 70 HUR or level 70 GUR card.

If you know you want to max the stats on a card, the worst option you can do is wait until it is max level.

Also remember that you can apply both the Attack and Defense arcana with a single material card.

Suggested Max Stat per Skill
Some cards don't need to have max attack, while others don't need max defense. If you have limited medals and wish to only select 1 stat to max instead of both, here are a few suggestions cased on card skill. In the end though, it depends on what other cards are in the unit that will determine which stats to max.

Reducing Cost for cards available for Awakening
If you want to reduce Gold cost of increasing ATK and DEF for a card that can be awakened, you can apply some of the arcana before Awakening.

The best way way to save gold is to calculate the number of Arcana needed to max the GSR or GUR stats, then apply half while the card is still HSR or HUR (starting at level 1), and the other half after awakening (again starting at level 1).

For example, using a fully amalgamated Chocolatier, the ATK at level 90 is 20904. So we calculate our needs as  . This tells us we will need 382 arcana to reach the max of the higher stat (ATK) on our Chocolatier. We would then apply the first 191 to the HUR version starting at level 1. After awakening, the card resets back to level 1 again. Now we apply the remaining 191 arcana to the GUR starting at level 1.

Many cards, like Chocolatier, have different values for ATK and DEF. In these cases, calculate the upgrade count needed based on the lower stat. Start upgrading that, by itself, until the the difference is accounted for, then apply both together. The stats may still not be equal as the unawakened card may have a different stat spread than it's awakened version.

Using this method, your HUR will end up between levels 40 and 50, then your GUR will end between 40 and 50 again. The total cost for the upgrade to max stats will be between 126000 and 165000 gold depending on how often a Great Success occurs during the upgrade.

If you had waited until the GUR was at level 90 to begin the upgrade, it would cost 729120 gold to upgrade Chocolateir

If you max stats at level 89 on the GUR Chocolateir it would cost 360640 gold and should still be on level 89 upon completion. That is about 49% of the gold from a level 90 upgrade.