Are there rules for melee with massive monsters

[Nebuul]

If our party of intrepid adventurers is facing a colossal-sized threat, are there any rules for things like AOE melee attacks and such, whether it is stomping on the players or just the club is the size of a building and will hit them all? Also, if a colossal-sized monster has combat reflexes and players run up to it, does it get attacks of opportunity for every square players run through that is threatened by its reach? Does it get attacks as something both leaves a square and enters a square?

Thanks!

[Ottriman]

Colossal monsters do not have AOE melee attacks in d&d 3.x.

At least not without special rules, trample allows it to potentially destroy a lot of weaker smaller enemies if it has it.

They do have incredible reach which means they can in fact get an incredible amount of attacks of opportunity with combat reflexes.

Overall though its no different than running a large monster but just with bigger space/reach/beatstick numbers in general. It would be really cool if the system had more detailed rules for combatants of very different sizes doing things like clambering over the larger one or something but sadly those are lacking.

[Uncle Pine]

If our party of intrepid adventurers is facing a colossal-sized threat, are there any rules for things like AOE melee attacks and such, whether it is stomping on the players or just the club is the size of a building and will hit them all? Also, if a colossal-sized monster has combat reflexes and players run up to it, does it get attacks of opportunity for every square players run through that is threatened by its reach? Does it get attacks as something both leaves a square and enters a square?

Thanks!
Special abilities such as Crush (http://www.d20srd.org/srd/monsters/dragonTrue.htm) and Trample (http://www.d20srd.org/srd/specialAbilities.htm#trample) and feats such as Area Attack, Crush and Thunderclap (all from Savage Species) allow a big creature to hit multiple opponents with the same attack. War Hulk (Miniature's Handbook) also gets similar abilities that she can use with iterative attacks.
Combat Reflexes does not let you make more than one attack for a given opportunity, so even a Colossal monster will only be able to make a single AoO for each move action its opponents make to move out of a threathened square. Source (http://www.d20srd.org/srd/combat/attacksOfOpportunity.htm).
Only leaving a threathened square triggers an AoO, not entering one. See above.

[Nebuul]

Only leaving a threathened square triggers an AoO, not entering one. See above.

Right, but as they pass through squares, they are leaving threatened squares, hence my confusion.

[Allanimal]

Right, but as they pass through squares, they are leaving threatened squares, hence my confusion.

Not quite sure where it says this in the SRD, but the PHB p.138 states "Moving out of more than one square threatened by the same opponent in the same round doesn't count as more than one opportunity for that opponent."

Edit: Oh, I've found it. Its the 2nd to last sentence on the page Uncle Pine linked to.

[KillianHawkeye]

Right. It's not even per Move action as Uncle Pine said, it's per round. You can take a double move on your turn and only provoke a single AoO from each enemy you pass regardless of where exactly your first Move ends and your second one begins.

The benefit of having Combat Reflexes and a high reach isn't to take several AoOs on a single enemy, but to be able to consistently get AoOs on several enemies every turn.

[Uncle Pine]

Right. It's not even per Move action as Uncle Pine said, it's per round. You can take a double move on your turn and only provoke a single AoO from each enemy you pass regardless of where exactly your first Move ends and your second one begins.

You learn something new every day. I've always thought the AoO was per action, even for movement actions. Thank goodness it probably never came up during a session.

[Kayblis]

Although there aren't AoE melee attacks as a maneuver or feat in 3.5, you DO have a case where such things exist. I suggest you look up the War Hulk prestige class from the Miniatures Handbook, as it has some nifty class features that can be given to large monsters as homebrew feats. Namely, Great Swing lets you hit 3 adjacent squares with an attack as a full-round action, Mighty Swing lets you do it as a standard action and Massive Swing attacks all squares the monster threatens as a full-round action. As an extra, the class also has some rock-throwing abilities that let him throw big boulders and affect large areas.