Attacks versus immobile/helpless characters are 'autocrits' in 4e. Hacking on the head/neck of an 'dead' enemy doesn't sound harder for me.
Sorry for being argumentative, but this sounds very un-4e for me. I enjoy something like this in AD&D, but dislike to meshing systems to much.
May I suggest something like a skill challenge? Some try to hold down/ bind the ogre while the other roll their attack bonus instead of a skill?
Maybe 5 success before 2 failures. And all that while someone else has to occupy the other active ogre.
If we fail the ogre is fully up again and we have to retry once it is dead again.
Just a suggestion, but this uses a bit more the 4e system. Scratch it if you dislike the idea.
Grim is fully fine with fleeing instead
Hmmm...
I just looked again through the rules and I see the following-
Helpless
While a creature is helpless, it grants combat advantage and can be the target of a coup de grace.
&
Coup de Grace
Sometimes, you have the opportunity to attack a foe who is completely defenseless. It’s not chivalrous to do so, but it is viciously effective. This action is known as a coup de grace.
COUP DE GRACE: STANDARD ACTION
Helpless Target: You can deliver a coup de grace against a helpless enemy adjacent to you. Use any attack power you could normally use against the enemy, including a basic attack.
Hit: You score a critical hit.
Slaying the Target Outright: If you deal damage greater than or equal to the target’s bloodied value, the target dies.
So...
From the above you get Combat Advantage, you still have to make a To Hit roll, if you hit you do a Crit- is that right?
My problem lies in the fact that the creature has no HP, it's dead- therefore I suggested a much easier To Hit, with the above rules you just get a +2, unless I'm not seeing it right- feel free to step in, I'm very reliant on the compendium here.
In essence that would mean you need to hit AC18 (if you were targeting AC) to hit the Zombie Ogre... using the above rules.
My suggestion was to make it all defences 10- I figure you can hit the thing.
The creature has no HP so you can't coup de grace it, you can't kill a dead thing until it is alive- if you see what I mean.
I had in mind a number of HP to hack through a limb, I was treating the creature as an object- it has low defences, and a set number of hit points to destroy (sever).
I have no problem with questioning the rules, likewise I have no problem with making this a Skill Challenge (as suggested). I would however like to work out where my above interpretation went wrong, just because I like to learn.
And of course I don't think you're being argumentative, this is a group game in which a lot of the rules are subject to interpretation- particularly as they do not cover such eventualities as- chopping through dead, soon to be not dead, Ogre Zombie's limbs...
Please reply then I'll make a ruling.