As you wait in your hidden positions, the charmed goblin follows Oloc's command and opens the trap door, descending into the basement. After a moment, from within the basement, you hear what sounds like a loud clinking of glass bottles. Then a door opens and slams shut again.
Two minutes pass.
Two more minutes.
Then the sound of a door opening.
And slamming once more.
More glass clinking.
Then grumbling voices, that by their tone, sound half annoyed, half expectant (OOC: Oloc alone can make out statements to the effect of "This had better be good, Dirtbag!")
You hear the trapdoor close with a bang.
The charmed goblin leads the way, followed by five of his companions out of the building ruins. All five are armed with bows and a variety of one-handed melee weapons. They step into the area you intended as a kill zone, and one of the goblins seems to interrogate "Dirtbag" on the other sentry's absence, but as he does so, Varros' and Duran's first arrows are already in flight.
Unfortunately, the twang of the bows is enough for the goblins to react. Duran's first shot catches only the tunic of the first goblin targeted, and then all the goblins dodge, duck, roll, and flop themselves on the ground and all the arrows miss their targets. "Dirtbag" however, has remained standing, perfectly still, through it all.
The goblins, a bit confused, look from your positions to "Dirtbag" and back again. Suddenly understanding, and growling with rage, they quickly get to their feet.
Surprise Round (ambush, surprise on 1-5; d6 = 3)
Duran: d20 = 10 + 2 (short) = 12 (miss); 6 + 2 (short) = 8 (miss)
Varros: d20 = 8 + 2 (short) = 10 (miss); 3 + 2 (short) = 5 (miss)
Sorry, guys. The dice were definitely unkind there. I'll switch to my translucent blues for you on the next round. :)
Also, just so you have a rough sense of how I handle situations like the ruse where the outcome is not certain, I set probabilities that the plan would succeed beautifully, succeed/fail partially, or fail badly (modified by things you did, like re-equipping the charmed goblin, and Oloc's story, both of which modified the die roll in your favor). I rolled a die, which determined the outcome (success, the ruse worked). Then I set a range of how many goblins your charmed fellow would succeed in bringing out, based on your revised intent to draw out five, and the possibility that your charmed inside man would get that exact number, or fewer, or more. Again I rolled the die, and bingo – five exactly. To determine how many brought their bows, I set a range from zero to five. And again rolled five exactly.
Sometimes, like your initial ambush of the two sentries, the plan is solid and there are few variables, so I'll simply rule that it succeeds. Other times, if there are "dicey" factors (substantial elements beyond your control), I'll use the dice. When I use the dice, there will always be a chance of success, of failure, and (if applicable) of something in between.