Hideous Laughter: What actions are available?

Question

Ah Tasha's Hideous Laughter, or simply Hideous Laughter in Pathfinder.

My monster's fell fast and hard to this spell last night, and though it was a wonderful victory for the PCs, I'm now filled with trepidation at the apparent power of this 2nd level spell.

My first question revolves around the possibilities for the afflicted character/monster, the spell reads [emphasis my own]:

This spell afflicts the subject with uncontrollable laughter. It collapses into gales of manic laughter, falling prone. The subject can take no actions while laughing, but is not considered helpless.

Now, a helpless character means:

A helpless character is paralyzed, held, bound, sleeping, unconscious, or otherwise completely at an opponent’s mercy. A helpless target is treated as having a Dexterity of 0 (–5 modifier).

So, since they aren't helpless and they can't take any actions...what exactly can they do once they succumb to Hideous Laughter? -- Can they move/stand up? Shift? Take attacks of opportunity? Defend themselves?

Answer 1

Hideous Laughter can mostly be summarized as "fall prone & skip your turn"

As you noted, the target can take no actions while laughing.

Moving is an action (PFSRD):

The simplest move action is moving your speed.

So is standing up (PFSRD):

Standing up from a prone position requires a move action and...

Taking a 5-foot step ("shifting" in 4e parlance) is an action as well, albeit a weird one (PFSRD):

Miscellaneous Actions
The following actions take a variable amount of time to accomplish or otherwise work differently than other actions.

Take 5-Foot Step
You can move 5 feet in any round when you don’t perform any other kind of movement. Taking this 5-foot step never provokes an attack of opportunity. You can’t take more than one 5-foot step in a round, and you can’t take a 5-foot step in the same round that you move any distance.

You can take a 5-foot step before, during, or after your other [emphasis added] actions in the round.

Attacks of opportunity are not actually actions of any sort (not even immediate actions) as far as I can tell, so the target can take attacks of opportunity by RAW (PFSRD), though this GM would deem that an oversight and disallow AoOs as well.

An attack of opportunity is a single melee attack, and most characters can only make one per round. You don’t have to make an attack of opportunity if you don’t want to. You make your attack of opportunity at your normal attack bonus, even if you’ve already attacked in the round.

An attack of opportunity “interrupts” the normal flow of actions in the round. If an attack of opportunity is provoked, immediately resolve the attack of opportunity, then continue with the next character’s turn (or complete the current turn, if the attack of opportunity was provoked in the midst of a character’s turn).

The part about not being helpless appears to be there to clarify that the target takes no defensive penalties beyond those imposed by being prone (PFSRD):

The character is lying on the ground. A prone attacker has a –4 penalty on melee attack rolls and cannot use a ranged weapon (except for a crossbow). A prone defender gains a +4 bonus to Armor Class against ranged attacks, but takes a –4 penalty to AC against melee attacks.

Answer 2

There is very little you can do

Namely, things known as not an action in the system, such as thinking, breathing, and passive checks. To list a few:

• Defend yourself against attacks. This is represented by your AC, which in this situation does not remove your dex bonus to AC, so your character is still passively trying to dodge attacks normally;
• Make a saving throw. This is always available, unless a specific rule says otherwise, and you can make a save even if you are unconscious;
• Make Knowledge checks;
• Make a passive Perception check to react to visual or auditory stimuli;
• Make a Sense Motive check versus a Bluff check against you;
• Activate the human feat Heroic Will;
• Activate your halfling's Adaptative Luck (alternate racial trait);
• Dismiss the Ironskin spell when absorbing a critical hit or sneak attack;
• Decide to accept or not a Skald's Raging Song;
• Activate a Mnemonic Robe (but not cast the spell);
• Use a Hero Point (optional rule), as this is clearly stated as not being an action to use.

Everything else, from standard to move to swift to immediate, and also free actions, are out of question. Your character cannot do any of those things that require any of the common action types.

Answer 3

To add onto Oblivious Sage's answer, I will focus on some other options you (or your creatures) have to better their chances preemptively against this spell (in case it is trivializing your encounters.)

As far as a second level spell goes, it can be very effective. However it is only single target, and they get a second save next round to resist its effects. It also works best on creatures of the same type. Meaning (assuming standard humanoid problem) that a non-humanoid enemy will not be as worried about this.

But wait! Their enemies are human! How ever can we stand in the face of these hideous jokes? Well, they cant make all of us laugh! Lets go as a team!

Since this is a single target spell, your caster will have to pick and choose targets to disable, and will have to more carefully decide who needs to be taken out (this adds a layer of strategy to the combat as well, potentially making it more engaging).

If the enemy party has a bit of variety and has some people who have better will than fortitude or reflex, they would have a better chance to remain stoic in the face of hideous hilarity. This has the benefit of making the PCs reliant on eachother as one character cannot (as easily) swiss army knife their way through every encounter!