It can looks like traits system. Some troops can have, some not, passive effects like:
-susceptible for poison: if troop is poisoned loose 2 health each turn
-susceptible for skull attack: take additional damage from skull match
-panic: if troop loses his armor it take only half of mana from gem matches
Thats only examples, there can be many possible effects just imagine yourself, it could bring some variety to this game.