How many of each card should I keep?

[Omnior]

I've read that you really only need 12 of each card:  6 to upgrade, and 6 to keep un-upgraded.  Is this idea true for rare weapons and other rare cards, or should I, for example, keep all of the Owl's Eye cards I win?  I believe I have around 20 Owl's Eye cards already  .

[JonathanCrazyJ]

You never need more than 6 upgraded and 6 unupgraded of any card, because you can only play a maximum of 6 in a deck. Feel free to sell 8 Owl's Eyes

[ARTHANASIOS]

You never need more than 6 upgraded and 6 unupgraded of any card, because you can only play a maximum of 6 in a deck. Feel free to sell 8 Owl's Eyes

^this

maximum of every card type is 6. Keep 6 unupped for PvP events like Weekly Tournaments and 6 upped for grinding and for some other PvP events too (like upped Weekly Tournaments)!

[Espithel]

It's also more efficient on electrum to keep everything instead of selling all your non-rares and buying what you need when you need it.

[Omnior]

Thanks for the replies!   It looks like I will shortly have the coin to upgrade a fair number of cards after I sell off all the rares I have over 12.