You start out down by the creek, beyond which lies a house. Five-foot tall grass covers the ground for 100 feet before opening into a nicely trimmed lawn dotted with small trees. Two guards are on duty. One stands at the front door, while the other leisurely walks the perimeter near the edge of the tall grass.
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Facts about the map:
* Standing in a square of tall grass provides concealment.
* Standing in a square with a small tree provides cover.
Concealment
If you want to stealthily approach the house, you can make a Stealth check as you Move through the tall grass. This is allowed because you have concealment. Your Stealth roll is opposed by the guard's Perception. Since the guards are on duty and actively looking for enemies, they get to make active rolls. The DM might require you to make a Stealth roll for each Move action you take, or he might let you get by with one check as you advance through the tall grass. When you get to the edge of the lawn, you stop in the last square of tall grass. You still have concealment and can remain hidden. The DM may require a new Stealth v. Perception test.
At this point, you cannot move onto the lawn without being seen unless you can maintain cover, concealment, or create a distraction.
Attacking From Behind (Distracted Creature)
Staying in the tall grass, make a Stealth roll and Move around the house so the guard at the front door no longer has line of sight to you. Then wait, hidden, until the patrolling guard makes his way to you. He gets a Perception roll against your last Stealth roll (or the DM may have you roll again). If you remain hidden, wait as he walks by you. When his back is to you and he is walking away from you, make a Stealth check as you Move out of the grass and up behind him. He gets a Perception check to notice this. If you remain hidden, you can attack and have Combat Advantage. You could then spend an Action Point to make a Stealth roll as you Move back into the tall grass. This is allowed because you end your move with concealment.
More than One Observer
Note that this is a form of distraction, since the guard is not in combat and is paying attention in a different direction from you. Further, if there was another guard that you hadn't noticed, maybe watching from the roof, he would automatically see you as soon as you stepped out of the tall grass to attack the patrolling guard. If you had stayed in the tall grass and silently attacked the patrolling guard as he walked by, the DM might have allowed you to make a Stealth roll as part of your attack. The guy you attacked would automatically notice you, but the guy on the roof might not.
Create a Diversion (Distracted Creature)
When you get back around to the front of the house, you can see the guard at the front door. He gets a Perception roll vs. your last Stealth roll. If you move out of the tall grass, the guard will see you because the squares you must cross are empty -- they provide no concealment or cover themselves. You throw a pebble to create a distraction. Make a Bluff roll against the guard's Insight roll. Then, when the guard is looking the wrong direction, make a Stealth roll as you Move to a square with a small tree. If you were unable to end your move in a square that provided cover or concealment, the guard would automatically see you.
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This is right by RAW as near as I can tell. Gotta love little thought excersices like this.