About the characteristics of heroes

Where can I see the characteristics of heroes (cards)?

You can find out about the stats of any hero by studying this table https://docs.google.com/spreadsheets/d/1WEiJ80nyOaxWQS0zLwvqomO3L0Ko1avOIW8PW8OfOfE/edit?usp=drivesdk
As for the next tool, it was created by a community member named Nor4eG. Here you can calculate the strength of your team (which consists of 5 same/different cards), as well as estimate the probability of winning a particular campaign.
Also, the existing characteristics of the hero (level, health, attack, etc.) are contained in the blockchain, so they can be viewed on the page of each card in the AtomicHub (section Mutable attributes)

Why are stats not displayed on some cards?

This information is not available only for those cards that have never been in game. After the very first add/withdraw-action (plus some action with card in game) such a card is given characteristics.