The ambush will take place in a city of late medieval Rhudaur, a successor state of Arnor in the MERP setting.
I also let the experienced members direct the hiding of the others and mark a KZ, Vladimir.
My doubt is whether the archer who has 8 attacks won't take me all the assassins before they snipe her as she's got a very high Long bow OB, and QU for Initiative. I think as Dale said that if she's got no line of sight she can't detect the rogues shooting from the back only those from the front.
You could say that she'll look back, but then unless she gains a Perception contest (she'll have to win a Perception roll - the Perception of the foes) she loses initiative for the archers in the back. If she doesn't make it, then either she loses Initiative or is surprised, losing the DBs.
Urban ambushes are even deadlier than those in the wild. The only real deterrent is that most cities frown upon fighting in the streets so unless the local constabulary has been bought off, such an event is not ignored.
I could say that
my entire six years in the military was devoted to RPG research as I enjoyed two years in Germany exploring Medieval cities and examining the architecture, street layouts and historical features that figured into warfare from the Dark Ages to the present (as a Communist invasion was expected during the Cold War era).
World War Two German snipers were particularly effective at using Medieval architecture to their advantage: The tile roof of a German building or cottage is actually a light wooden frame that the tiles simply rest upon. Remove one or two tiles and an effective firing lane can be opened along a set line of sight that cannot be easily detected, especially from other angles. A sniper would then set up a shooting stand a few meters from the hole and be able to take multiple shots while undetected. A series of snipers with similar firing lanes that cross the KZ up, down and laterally would be easy to set up, as the shooting stands would be located in the upper attics, with commanding views.
An urban ambush in an active city is far more deadly -Unlike a wartime scenario, the enemy force won't be at full battle awareness. There may be random civilians in the area, or even hostile confederates who can attack targets to keep them adequately distracted so that they cannot use their Perception effectively.
To limit the targets' mobility, heavy carts can be emplaced ahead and behind the path of travel, moved into place and brakes locked. These can be turned into small fortresses and close-range sniper positions (this is the Hussite
Wagenberg, which I have used multiple times in past games, and in WW2 terms the Russians used
Tachanka machinegun carts to the same effect). Every building lining the street is a potential sniper's position or storm infantry hideout. The following ambush group could also take up positions on or behind the rear heavy cart and attack from partial cover.
If there are mounts, have the lower skilled archers target those, as they will have lower DB. The more confusion the better and controlling wounded or dying animals will reduce the combat effectiveness of riders. I'd toss pots of predatory animal urine or blood into the streets to further frighten their mounts. (In one campaign, my character with a Hvy crossbow teamed up with a siege arbalest NPC who would target mounts while my PC killed the rider while in mid-fall and unable to defend themselves. They had servants who loaded additional weapons and had them ready in order to keep up a frightening rate of fire).
In an urban setting, cueing the ambush is actually far easier as the go signal could be as innocuous as waving a blue handkerchief...
In my gaming club, it was a regular practice for a GM to employ other players as OPFOR (Opposing Forces) to counter powerful players. In this practice of sanctioned PKP, players were put to a real test of skills and command against PCs, not disposable NPCs. We used this method to crush small parties up to military units of divisional strength with varying success. I've even used this on my own "gods of the battlefield" players who eventually bit off far more than they could chew, despite my constant warnings.
The best way to teach a PC a valuable lesson (or kill them) is to use another PC.