Socket Card Upgrade

You can convert 10x lower grade Cards into higher grade Cards at the Card Master NPC. There is a success probability depending on the % of the Cards. A Cash Shop item ‘Scroll of EProtect’ (green scroll in the picture) exists to prevent the loss of Cards in case of failure. Note that you can do up to 99 attempts in one click if you put enough items in the slot.

Tip: Regarding 3% upgrades only Lightning Card 3% to 4% is worth the costs. Success rate 15%.
When you try to upgrade a 4% card to a 7% card you should definitely use a Scroll of EProtect.
Success rate 4%

All suit Piercing cards

Note: 2%, 3%, and 4% are droppable from monsters +20. The 7% cards are only obtainable by upgrading x10 4% Cards to 1x 7% cards at the NPC ‘Card Master‘. 

All weapon and shield Piercing cards

Note: D

Card Level Fire Earth Water Electric Wind
D
STR +2
STA +2
INT +2
DEX +2
Speed +2%
C
STR +3
Crit-DMG +1%
STA +3
INT +3
D. Casting Time + 1%
DEX +3
Crit Chance+1%
Speed +3%
Attack-Speed +1%
B
STR +4
Crit-DMG +1%
STA +4
INT +4
D. Casting Time + 1%
DEX +4
Crit Chance+1%
Speed +4%
Attack-Speed +1%
A
STR +7
Crit-DMG +2%
STA +7
INT +7
D. Casting Time + 2%
DEX +7
Crit Chance+2%
Speed +7%
Attack-Speed +2%