Skunk: Life, perhaps, with a Darkness or Air ability. The ability type depends on the mechanic. With the cloaking thing, that would have to be Darkness for the actual Cloak card.
Mongoose: Good for poison counters. Since poison is common, then it's good.
Porcupine: Since actual porcupines curl up into a ball, might the opponent take damage when it damages porcupine? Well, damage but not kill, to balance.