A worry about "special case monster abilities"

[delericho]

Freeform systems are even worse when trying to make a core game that is easy to learn.

I disagree. IMO, a single freeform system is going to be easier to memorise than a hundred special cases, all with slightly different unique mechanics.

In any case, to deal with this you do two things:

1) Produce a "D&D Basic Set", that includes the basic combat rules, but doesn't include the freeform system for stunts. That way, new players learn the rules in an easy-to-digest form, without having to worry about either special cases or a stunt system, and then they get to graduate to the 'real' game and find that the knowledge they have acquired is still valid because the systems are 100% compatible - the 'real' game just does more.

2) In the first chapter of the PHB and the DMG, insert advice on how best to learn the game. Include things like "Read the basic rules, and then play a few sessions. Then read the advanced rules, and gradually add them". That done, clearly mark the stunt system as "Advanced Rule".

So, if this system is granting the ability to duplicate the class powers of a specific power source (martial; Power Attack and Disarm are both powers, as far as we know) only, then what is the point of those classes? If they have more powerful versions of the "stunt" Power Attack and Disarm, they lose distinctness and revert to the previous edition standard of "just better at what everyone can do, rather than having unique powers."

They shouldn't be powers, and the previous systems were better in this regard. It is simply absurd that a 30th level Paladin cannot even attempt to disarm Random Orc #3, simply because Disarm is a power reserved for Fighters.

Again, it denies a lot of niche protection to fighters, while firmly supporting it for spellcasters.

The necessity of niche protection is vastly overrated. Beyond extremely low level, you will never see the Wizard attempt a Disarm, Chandelier Swing, or other martial stunt, because the character is so bad at these things as to make it pointless to even try. The niches are better protected just fine by specialisation.

Your Chandelier Swing and Table Slide are examples of what a specific skill (Acrobatics) can do, rather than some vague freeform stunt system.

Yes, they're examples. Along with all the other examples I provided, they're meant to show the range of things that should not be powers, but rather should fall under the aegis of the freeform stunt system.

I might not be able to, but my friend Jason is capable of it, since he was the guy that put two paintballs into my leg, which caused me to shift my stance and expose my head to a face shot. The hostage was untouched.

He did it once, safe in the knowledge that if he missed, it was no big deal. Can he do it every time? Would he even take the (head) shot if he was using real bullets?