What do the card symbols mean?

[Illuminati MLG]

https://imgur.com/DSF9vDP

I get the different colors, but what is the difference between the full red card and a black one with border?

Also, the number to the right of it is an indicator for difficulty, right? Like the skulls were in Thea 1?

[DNLH]

Filled cards mean that damage taken during the challenge will stay on characters and can potentially kill them. The outlines mean that damage taken won't stay and it is simple matter of win/lose. Think of it like of combat vs. non-fighting (sneaking, hunting etc.) challenges from Thea 1.

The number is general indication of difficulty, yes. It's not always right, though.

[minimen456]

Thanks. Devs should make a tooltip on this matter :D

[Francisism]

I thought it was the number of cards the enemy have. It was so confusing when I fight enemies expecting that they only have 3 cards to choose from.