Stinger is one of the best allies. Why? Well you got 1 atk or thw and a block. It´s unlikelly that you will have 3 allies in play but if you do you can play her anyway with no need to discard one ally. Sure, you need the avenger trait to play it but there are plenty avengers anyway. Furthermore, Avengers Tower or Team-Building Exercise let´s you play it for free. Insane card.