Add Guard as a basic action?

[Liir]

I think we need a new basic action to carefully watch an area and/or enemy.

Guard (Basic Action – 1 action)
You are actively scanning for threats and prepared to take advantage of strategic openings. You can use the Attack of Opportunity reaction until the start of your next turn. Using the Guard action is apparent to all observers. You cannot Guard when you are flat-footed. Using this action ends your turn.

What does this give us?
• Adds the capability to use the threat of an opportunity attack as a tactical decision (with a cost) to all characters.
• Allows quicker decision making for players during combat -- because you know who is guarding and can perform an opportunity attack.

Mechanically, Guard is the same as readying an action to strike, except in exchange for being limited to a specific trigger: “A creature within my reach uses a manipulate action or a move action, makes a ranged attack, or leaves a square during a move action it’s using”, it costs 1 action instead of 2 actions.

You could adjust the Fighter class feature for compatibility, replacing Attack of Opportunity with something like Combat Awareness. Combat Awareness: You can use the Guard action as a free action at the end of your turn. Attack of Opportunity would gain the prerequisite “You are guarding” and be added to the list of Specialty Basic Reactions (page 309).

You could add a Guard (action) trait and apply it to defensive actions. Guard trait: When you use an action with the Guard trait you can use the Guard action as a free action at the end of your turn. Some actions that could qualify for the Guard trait: Raise a Shield, Dueling Parry, Twin Parry, and Parry (from the weapon trait).

[Deighton Thrane]

I think there's a number of issues this, especially when balancing it against other actions. Most prominent is probably the fact that the way accuracy works in second edition means that any attack at a -10 penalty is nearly impossible against level equivalent monsters. So trading an attack at -10 for even a chance at an attack at a -2 is pretty much always better in certain circumstances. It's also much more efficient than readying an action, which also takes your multiple attack penalty, even though it's an attack that happens outside your turn.

Considering readying an action is already a thing, I don't really see the purpose to this, other than to give attacks of opportunity to every character. The design paradigm in second edition seems to indicate that every class's special reaction ability should be unique, or at least that it should be limited to only a few classes, and this seems to pretty blatantly violate that design goal.