The monsters with the saw on them generally need to go in the first position. For most rulesets they can't strike from back positions. The exception to this is the monsters that have the green claw displayed on them. They can strike from the first and second position. Sneak Monsters can strike from any position. When playing its usually best to place a high life monster in first position. Range monsters should be in the back as they can't strike from first position. Magic can strike from any position.