Hard counter -- a pet using attacks that the other pet is vulnerable to.
Example: A Young Talbuk using Horn Gore against a Rat
Soft counter -- a pet resistant to the other pet's attacks:
Example: A Darkmoon Zeppelin is resistant to all Arcane Eye's attacks
Double counter -- a pet both resistant and harmful to the opponent
Example: A Lil' Bad Wolf -- resistant to Black Lamb -- using Claw
I also wonder if are there names for the other, not exactly desired dependencies?
Apart from "total fail" situations where we just focus on the other pet, there are also two "middle" cases:
1. A situation when both pets are the hard counters of each other.
Partially a good thing to keep in mind when we can't know what pets are the opponents.
Example: Widget the Departed is vulnerable to Black Lamb's attacks, but can take a revenge using Pounce.
So how to call each of them? A blood counter, maybe?
2. A situation when both pets are the soft counters to each other.
Quite difficult to meet and not desirable anyway.
Example: It's so hard to find that I need to ignore some possible abilities, but Kirin Tor Familiar and Darkmoon Zeppelin.
A --- counter? No idea about this one.
I don't know how to end this post so I just wish you that you had a nice day.