Combat Speed

The speed bonus from Combat Speed applies to all movement types for which you have a base speed listed (whether that speed be land movement, burrowing, flying, climbing or swimming). Use this improved base speed when calculating your movement rate for movemene types based off your base speed.

For example, sahuagin have both a listed land speed and a swim speed. A sahuagin harrier would gain the benefits of combat speed on both these movement types. If that harrier wanted to climb something, he would do so at 1/4 of his improved base land speed.

Mobile Assault

Q: Does the harrier weapon bonus apply to all melee and ranged weapons under mobile assault?

Yes.

Rapid Assault

Q: Do Rapid Assault and Manyshot stack?

From Rapid Assault: "you must carry a light or a finesse weapon to use this ability".

So the answer is yes, but only for thrown light or finesse weapons (projectile weapons are neither light nor finesse) and only for as many weapons as you can throw without using a move action to draw one (so unless you have quick draw or more than two arms, the fact they stack won’t help you much).

The penalties to hit stack, of course, just as the number of attacks does.

Running Assault and Superior Running Assault

You can combine the effects of other Harrier class abilities with Running Assault and Superior Running Assault, even though these are full round actions, because they are treated as being "two actions in one". This is defined in Running Assault. Since Superior Running Assault is an extension of that ability, the same base assumptions apply. Superior Running Assault wouldn't be very superior if it nerfed the advantages offered by Running Assault!

What SRA is intended to do is give you the usual benefits of Running Assault, but with the ability to use your full attack routine instead of just a single attack. Think of it as a move action + a standard action that happens to gain a bunch of bonus attacks based on your BAB.

Q: Can you use Superior Running Assault in conjunction with Whirlwind Attack to strike every foe you move past (and consequently threaten)?

By the rules, yes. But I would suggest that you run it in much the same way as the Weapon Master's Mobile Assault ability: each opponent threatened can be targetted only once in the round, and you must resolve all allowed attacks against each target before moving on. Even with this limitation, the ability is very powerful.

Steel Dancer

Q: What are the advantages of Steel Dancer compared to using Tumbling Attack?

Steel Dancer's main advantages are that:

(a) It lets you move through an opponent without Attacks of Opportunity (you'd normally need to use Tumbling Move for that, which would be a simultaneous action with the Tumbling Attack and apply a -5 penalty to both Tumble checks).

(b) It combines (most of) the effects of Tumbling Attack with the effects of Tumbling Move and Dodge Foes, all as one action (you move through a threatened area, avoiding Attacks of Opportunity as per Dodge Foes, then enter the opponent's square, which requires Tumbling Move, then deny him his active defence, per Tumbling Attack). Normally, you can't do three things as one action.

(c) Steel Dancer allows you to move both before and after your attack, which you can't do with Tumbling Attack unless you have Mobility 3.

Harrier Movement-based Benefits and Full Actions

A harrier who moves while performing a full round or full attack action (such as when charging, performing a stunt or using Mobility Expanded Mastery 3) still gains the benefit of their movement based abilities such as Mobile Defense and Mobile Assault. The "move action and standard action" wording in the harrier class abilities is not intended to disallow that.

Note however that a Harrier who uses the Run full round action loses his Active Defense Bonus (unless he has the Run feat) and therefore gains no Defense bonus from these abilities.

Counting Squares for Harrier Movement-based Benefits

Q: I think some mention should be made about how diagonal movement plays with the Harrier's movement abilities. I assume that diagonal movement counts as 1.5 squares for these purposes?

Also, can a harrier charge and use his abilities - eg. mobile assault? How about running and mobile defense?

For Harrier abilities, every 2nd diagonal square counts as two squares moved, just as it counts as 2 for the purpose of counting movement used up. The reference to 'unique' squares is to stop characters from moving 5 ft left, then 5ft right, then 5ft left, then 5 ft right, then 5ft left, then 5 ft right, and claiming they moved 6 squares. It's not intended to force the Harrier to only make 90-degree turns :)

A harrier may charge while using mobile assault or defense.

Harrier Movement-based Benefits and Base Attack Checks

See Base Attack Checks for details.

Harriers and Mounts

Movement on a mount counts for getting Harrier movement bonuses. Consider your move action to be directing the mount.

A harrier can get good bonuses from a mount's high movement capabilities, but remember that mounts are very fragile and easily lost in combat (unless a lot of feats get sunk into the Beastmaster feat chain, but then that's an opportunity cost to the character that a non-mounted harrier won't suffer).