All melee attack monsters can attack from any position" What does that mean exactly, to me it sounds like sneak ability but its not.

With sneak ability the monsters attack the last monsters of the opponent, but with the rule you described, you're own monsters can attack from any position, but will attack the first monster of the opponent.

I opened 18 Untamed packs recently :D

Pack openings are addicting, got me back to playing :D