Tank passive
Your basic attack gains +1 Knockback.
Units you knockback will Knockback other units.
Passives
Class passives and the Collarless pool, each with its upgraded + effect.
Data updated
Each regular class has 25 passives, while Collarless cats get a bigger pool of 64 that includes oddities like Worms, a 50% chance to spawn a maggot familiar when you end your turn. The Jester has just 2. Upgrades usually stack a second effect on the first. Frenzy gives +2 STR when you down a unit, and the upgrade adds +2 SPD.
Breeders build around this one. It shares your other passive with the party at the start of each battle, and the upgrade makes your kittens always inherit that other passive.
Fighter's Soul puts Fighter abilities into your level-up offers. Jester's Soul offers abilities from any class and gives two rerolls. Void Soul goes the other way and offers only upgraded Collarless abilities.
