Grab ability's -20 mechanics.

[Net-Soul]

The grab ability has a part that states the following:
"The creature has the option to conduct the grapple normally or simply use the part of its body it used in the grab to hold the opponent. If it chooses to do the latter, it takes a –20 penalty on its combat maneuver check to start and maintain the grapple, but does not gain the grappled condition itself. A successful hold does not deal any extra damage unless the creature also has the constrict special attack. If the creature does not constrict, each grapple combat maneuver check it succeeds at during successive rounds automatically deals the damage indicated for the attack that established the hold."

It sounds to me that when a creature accepts this -20 penalty it also maintains the grapple as part of its full attack by sacrificing the attack which it uses to maintain(also taking the -20 penalty to the maintain).

Is this a correct interpretation of 'penalty to start and maintain' part.

[Scott Wilhelm]

I think the creature has the option of making a 2nd round melee attack, then Grappling as a Free Action, and if successful, it inflicts damage. If the creature does not want the Grappled Condition itself, then it takes a -20 on the CMB.

or

Making a Maintain-a-Grapple Combat Maneuver Check as a Standard Action, or a Move Action if the creature has Greater Grapple and/or as a Swift Action if it has Rapid Grappler. Doing that, the Froghemoth or whatever has all the grappling options open to it.

So,

the Froghemoth lashes out from the water in the surprise Round with a full attack on the party: 4 tentacles, a bite, and its tongue. It scores 6 hits and 6 successful Grapples. It elects to accept the Grappled Condition itself, forgoing the -20 penalty.

The next round, the Froghemoth decides to take a Standard Action to Swallow Whole the character in the creature's mouth. It takes a Standard Action to do so. It does not have Improved Grapple, so this would normally provoke an Attack of Opportunity, but since the rest of the party are Grappled in the Tongue and Tentacles, they can't make Attacks of Opportunity. The first Character get swallowed, but then it has no more Actions left to Maintain Grapples, so it is forced to let the rest of the party go.

The next round, the Froghemoth elects to Full Attack again, and scores 5 more Grabs in 4 tentacles and its tongue, its mouth vacant for the moment.

The next round, it might decide to swallow the creature its holding in its tongue. I think it needs to make a Standard Action Grapple Check to Move the character from Tongue to Mouth. Under these circumstances, though, it would probably be better to Full Attack again, and if the Bite is successful, Initiate a new Grapple and transfer the character to its mouth that way, and all subsequent successful Grapple Checks from the other Attacks Damage the other characters, and unsuccessful ones release the characters.

If the GM wanted to be really mean, the Froghemoth would decide it had a full belly and retreat into the pond with its belly full of Barbarian...

[blahpers]

Net-Soul wrote:

It sounds to me that when a creature accepts this -20 penalty it also maintains the grapple as part of its full attack by sacrificing the attack which it uses to maintain(also taking the -20 penalty to the maintain).

Is this a correct interpretation of 'penalty to start and maintain' part.

No. The ability does only what it says it does. For the price of a -20 to the combat maneuver check to initiate the grapple and to all subsequent checks to maintain that grapple, the grappler does not gain the grappled condition. That's it. It's still a standard action to maintain the grapple unless the creature has some other ability that supersedes this (such as Greater Grapple et al.).

If you're wondering how that lets giant tentacled horrors grab multiple creatures at once and squeeze them to death over the course of several rounds, well, Pathfinder RPG just doesn't model that very well.

[gnoams]

Here's how I think it works raw:

Monster hits a person with an attack with grab. It can choose to 1, try to pick the person up with just that one appendage at -20, or 2, wrap all their appendages around them and grapple normally. If it chooses option 2, it can only pick up one person regardless of how many successful grab hits it has on different people. If it wants to pick up multiple people, it has to choose option 1. It could potentially hold up to one person in each of its appendages that has the grab ability. (So if it gets 5 attacks, but only 2 have grab, it can only hold 2 people).
If it chooses option 1, then subsequent rounds it still needs to take a standard action to maintain (at the -20), but it doesn't count as grappled, so it can make opportunity attacks (using any of its attacks not currently holding someone), and potentially pick more people up that way. It could also decide to stop taking the -20, shifting one of the people it is grappling from one appendage into a normal grapple and dropping any other people it might be holding.
If it chooses option 2, then on subsequent rounds it needs to use a standard action to maintain the grapple like normal. It can choose to try to shift the person from a full grapple to just held in one appendage by taking the -20 (and a standard action).

However, I've always run it where the monster can get its other attacks while holding someone at -20. I don't know if that's just cause what made sense to me, or if there used to be wording to that effect in 3.5. At any rate, the way I do it is if a monster is holding someone in one appendage, they can maintain that grapple as part of a full attack. They can only do a basic grapple (damage), not pin or swallow whole, or other maneuvers this way. Also when held in one hand, I count their cmd as 20 lower for the person to escape from. That's what makes sense and seems fair to me.