The whirlwind ability states:
Whirlwind (Su) - Some creatures can transform themselves into whirlwinds and remain in that form for up to 1 round for every 2 HD they have. If the creature has a fly speed, it can continue to fly at that same speed while in whirlwind form, otherwise it gains a fly speed equal to its base land speed (average maneuverability) while in whirlwind form.
The whirlwind form does not provoke attacks of opportunity, even if the creature enters the space another creature occupies. Another creature might be caught in the whirlwind if it touches or enters the whirlwind, or if the whirlwind moves into or through a creature's space. A creature in whirlwind form cannot make its normal attacks and does not threaten the area around it.
Creatures one or more size categories smaller than the whirlwind might take damage when caught in the whirlwind (generally damage equal to the monster's slam attack for a creature of its size) and may be lifted into the air. An affected creature must succeed on a Reflex save (DC 10 + half monster's HD + the monster's Strength modifier) when it comes into contact with the whirlwind or take damage as if it were hit by the whirlwind creature's slam attack. It must also succeed on a second Reflex save or be picked up bodily and held suspended in the powerful winds, automatically taking the indicated damage each round.
So, assume that the battlefield has 4 enemies spaced like the corners of a square, each 10' apart. The whirlwind has 90' movement. It can whirl through the spaces of those 4 enemies twice. According to the rules quoted above, it appears that any time the whirlwind "moves into or through a creature's space" there is a chance to be caught in the whirlwind.
Now, we might shrug and say, "Well, yeah, but 2 attacks on each of those guys? Meh. That's the rules, and since they have to fail two saves to be swept away, it's not that big of a deal." But... change the example just a little and it becomes super-cheesy: assume there is only 1 enemy. The whirlwind just zips back and forth over the enemy, gaining at least 9 attacks on the target. This forces 18 saving throws. In one round.
Sure, the creature that is in whirlwind form has to do fly checks to keep doing 180 degree turns to fly back & forth over an enemy, but most creatures that can do the whirlwind have HUGE bonuses to fly and will always succeed.
Visually, it makes sense that a target getting repeatedly bombed by a whirlwind would need to save repeatedly. But game-rules wise, is there anything to mechanically balance this, or limit it, or something? I'm wondering if I just missed a rule, similar to the trample limitations. (Trample has: "A trampling creature can only deal trampling damage to each target once per round, no matter how many times its movement takes it over a target creature.")
