Multiple movement modes in a single round

[Hirax]

Let's say a creature has a swim speed of 60, a fly speed of 150, and improved flyby attack. It wants to fly out from underwater, whack someone, and then fly back underwater. Are there any rules for how multiple modes of movement interact when used in the same round? I'm aware of ways you could hack it, by, say, ruling that if it swims 30 feet in a round, it can only fly 75, but I just want to make sure there aren't rules out there that someone is going to bring up when I run this encounter. edit: creature in question is a black dragon, for the curious.

[DegenPaladin]

I would personally rule that in a round that they wanted to use both, every square swum would count as 2.5 squares flown.

[BowStreetRunner]

I have generally understood that each move action uses a single movement mode (the modes listed beginning on page 90 of the rules compendium). So the activity you described would require one action to swim to the surface. Once there the character could use a fly move action to make a flyby attack and end on the surface of the water. Then another action would allow them to swim below the surface again. (Might help to have a Belt of Battle to do all of these on one turn.)

[Psyborg]

Alternatively, if attacking a target flying over water, one could simply use the Swim movement mode to Charge with Leap Attack (with wings giving a +8 racial bonus to the Jump check), falling back to the water as a free action after completing the attack.

Not technically using the Fly speed and Flyby Attack at all, and the target can't be as high as you could Fly (barring serious Jump-check optimization-fu), but it's slightly simpler, and it lets your attack count as a charge, with all the delicious things that come with that.

If the target isn't over water, this won't work too well. Although...for something like a deck crew of a boat it could still be done if you could Jump to them, Bull Rush them off [moving with them], and then fall back to water, effectively jumping over the vessel...it would also be a serious candidate for Crowning Moment of Awesome.

Keeping some form of move-as-a-Swift-Action in reserve is highly recommended to keep you from doing a belly-flop on the deck if your Bull Rush fails. Since you'd already be pumping Jump for this stunt, Martial Study (Sudden Leap) seems thematically appropriate, but any of the usual stuff (Travel Devotion, Belt of Battle, etc) is still applicable.

Now to stat up an Awakened Blue Whale Dungeoncrasher Fighter/Warblade/Bloodclaw Master and become the terror of the seas.