Hard counter -- a pet using attacks that the other pet is vulnerable to.
Example: A [pet]Young Talbuk[/pet] using [ability]Horn Gore[/ability] against a [pet]Rat[/pet]
Soft counter -- a pet resistant to the other pet's attacks:
Example: A [pet]Darkmoon Zeppelin[/pet] is resistant to all [pet]Arcane Eye[/pet]'s attacks
Double counter -- a pet both resistant and harmful to the opponent
Example: A [pet]Lil' Bad Wolf[/pet] -- resistant to [pet]Black Lamb[/pet] -- using [ability]Claw[/ability]
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: [pet]Widget the Departed[/pet] is vulnerable to [pet]Black Lamb[/pet]'s attacks, but can take a revenge using [ability]Pounce[/ability].
So how to call each of them? A blood counter, maybe?
2. A situation when both pets are the soft counters to each other.A [pet]Teroclaw Hatchling[/pet] is a blood counter of default aquatic pets when using [ability]Nature's Ward[/ability].
Quite difficult to meet and not desirable anyway.
Example: It's so hard to find that I need to ignore some possible abilities, but [pet]Kirin Tor Familiar[/pet] and [pet]Darkmoon Zeppelin[/pet].
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.