In the original Rolemaster, Ambush was one of the skills that worked differently than others. I’m sure at the time, they were just trying to fit a square peg in a round hole to get the desired result, but actually it was quit brilliant and should have been pursued in greater detail for other skills.
What do I mean? That the # of skill ranks can serve as a rule mechanic just like total skill bonus. RM made Ambush a skill rank only skill where the other skills were purely total skill bonus. But why not have both for all skills?
What does Ambush skill really entail? The skill description requires that the skill be developed with a specific weapon, but does that really make sense? Ambush is not about the weapon, it’s about surprise and the ability to target kill points on a body. A competent assassin can kill with a knife, a stapler or a pen by targeting soft spots or vulnerabilities. The type of weapon is irrelevant as long as it can physically carry out such an attack.
So what might be a way to handle Ambush using both # of skill ranks and skill bonus? Here is how we do it. The ambush skill bonus is used for the Offensive Bonus-no matter what the weapon or object. The GM chooses the attack chart/size based on the weapon and type of damage it might inflict (a flail would not be great in close quarters, while a wooden splinter would be great but do very little damage w/o a great attack roll). Obviously this is a close quarter attack, ambush shouldn’t work for missile, or thrown weapons (that’s a called shot with surprise bonus). The skill bonus reflects the versatility of training using any weapon or object to kill. Also, it recognizes that the ambush weapon is being used to kill with a direct strike and perhaps not how the weapon is normally used. If the attack is successful, then the # of Skill Ranks is used to adjust the critical roll. A bit different than the original rules: some would argue that this allows the assassin to use any weapon or object to kill a target. Correct.
In any event, that’s how we play it. does it seem overpowered? The Assassin would need to get into striking range without being detected (a different skill/ability), have some type of damage inflicting weapon, and generate a critical result attack.
Just my take, using my own hybrid system (S.W.A.R.M.). What’s yours?