Foil Action, unfortunately, provokes a lot of resistance from gamers - players and DM's alike. I've waded through all kinds of posts where the ability is declared to be simply broken and OP. You have to read through a lot of forum posts here in the den before the design philosophy starts to make sense, and even then it only makes sense in a mechanical, but not a narrative way.
It's not just the fluff of the ability. Sure, it doesn't make sense that someone could throw sand from 60 feet away and disable a beholder. But people will accept all kinds of stuff from marshals and white raven maneuvers and what not that is equally improbable.
I think the reason behind the resistance is twofold. First, Foil Action seems like counter-spelling, and fighters don't counterspell. There is a deeply rooted presupposition in the game that only magic can counter magic. Fighters have mundane class features, hence they cannot directly counter magic. (Aside from saving throws and hit point ablation, etc.) Plus it is a quickened counterspell that doesn't use up spell slots, doesn't require a check, and works not only against spells, but against anything that requires an action. It is much better than any counterspelling a wizard can do, and this runs counter to another deeply held presupposition, namely that anything that can be done by mundane means can be done better with magic. Also, melee cannot have nice things.
Now the great thing about the tomes is that they identify and reject these presuppositions. However I think that more needs to be done to eliminate their lingering traces in otherwise enlightened minds. And so I propose that Foil Action be modified to employ a mechanism that is similar to what is already accepted as appropriate to a mundane class.
Mundane classes can grant actions. Whether you are a marshal granting extra move actions or someone with White Raven tactics, you can give your allies extra actions. You'd think that this means you could deny your opponent actions, but the opposite of haste is not hold monster, but slow. What Foil Action should do is delay an opponents action, not deny it completely. Make it into a full-round action that takes effect just before that opponent's next turn. Give the party a chance to pile on it and kill it before then (or at least force the concentration checks that will result in it probably being disrupted), or get out of range, or to employ effective counter-measures (the cleric casting silence to prevent the Balor's blasphemy from going off, say).
I'd propose something like the following.
Drain Action (Ex): A 9th level Fighter may attempt to monkeywrench any action an opponent is taking. How does he do it? Not by throwing sand in a beholder’s eye, or batting aside a spell component, but somehow he does it.
He can negate a standard attack using Drain Action. If the attack was the first strike of a full-attack, however, the iterative attacks that follow are resolved normally. If a Fighter drains a charge, it is resolved as a movement followed by a standard attack; no charge bonuses apply.
An action that is not an attack or charge can be drained if it takes either a standard, move or swift action to complete. The affected creature may discontinue its action, or else try to complete it during the remainder of the round. If the action is discontinued it is wasted, and any spell slots, limited ability uses, or the like used to power it are expended. If the opponent attempts to complete the action it provokes an attack of opportunity; furthermore, if it receives damage before the beginning of its next turn, it must succeed in a Concentration check (DC 10 + damage dealt) or lose its action without result. If the opponent succeeds in completing the action it takes effect just before its next turn.
A Fighter must be within 30 feet of his opponent to use Drain Action, and must hit with a touch attack or ranged touch attack. Using Drain Action is an Immediate action. At 17th level, Drain Action may be used at a range of up to 60 feet.
He can negate a standard attack using Drain Action. If the attack was the first strike of a full-attack, however, the iterative attacks that follow are resolved normally. If a Fighter drains a charge, it is resolved as a movement followed by a standard attack; no charge bonuses apply.
An action that is not an attack or charge can be drained if it takes either a standard, move or swift action to complete. The affected creature may discontinue its action, or else try to complete it during the remainder of the round. If the action is discontinued it is wasted, and any spell slots, limited ability uses, or the like used to power it are expended. If the opponent attempts to complete the action it provokes an attack of opportunity; furthermore, if it receives damage before the beginning of its next turn, it must succeed in a Concentration check (DC 10 + damage dealt) or lose its action without result. If the opponent succeeds in completing the action it takes effect just before its next turn.
A Fighter must be within 30 feet of his opponent to use Drain Action, and must hit with a touch attack or ranged touch attack. Using Drain Action is an Immediate action. At 17th level, Drain Action may be used at a range of up to 60 feet.
I think a lot of the time Drain Action will work exactly like Foil Action; an opponent will choose to drop the action rather than accept the delay. That's fine- it's the opponent's choice. Some of the time (like when it has no other effective actions) it will accept the delay, and that gives the rest of the party something to do. Which is good - it's like a spellcaster who buffs his party members or controls the battlefield so they can do their thing. A fighter makes a threat manageable and empowers his party members.
tl;dr Foil Action is a great and much needed boost to the fighter, but it would be easier to swallow (and work just as good) if it delayed an action rather than denied it outright.
