I think I heard that you hit a skink in the front row first. If (when) it dies you randomize which column that skink was in, If the model behind it is a krox try and kill the krox, krox dies pick the skink behind and keep going.
when shooting you nominate a model to shoot at. So your apponent will likely choose a skink with a krox behind it. if it kills the skink it will then hit the krox.