In order to swallow a creature, you have to grapple them first. You can then attempt to swallow your prey after succeeding on a vore check while the prey is either grappled or partially swallowed.
As creatures become weaker, they are less able to defend themselves against hungry opponents. When a creature has taken more than 1/3rd its health in damage (lethal or nonlethal), vore checks gain a +2 against them. When a creature has taken more than 2/3rds of its health in damage, vore checks instead gain a +4 against them.
Swallow: You attempt to swallow the defending grappler. You can use this action on any creature that you have already grappled or have partially swallowed. Make a vore check against the enemy, factoring in all relevant bonuses. You get all bonuses that apply to vore checks, as well as a +5 due to controlling the grapple initially. A success by the predator moves the prey from “grappled” to “partially swallowed”, or “partially swallowed” to “swallowed”. Predators do not take penalties for grappling while prey is swallowed or partially swallowed, but may be subject to stuffed penalties when prey is swallowed or partially swallowed. A failed swallow check does not change the prey's status in either direction.
Predators that are more seductive than strong also have a way to eat prey of arguable willingness, either in or out of combat. To begin with, a predator may make a diplomacy check against a prey that is already at a friendly attitude or above, either by prior diplomacy or a charm spell, opposed by the higher of the prey's sense motive or will save. (A GM can have a predator make an intimidation or bluff check with appropriate penalties instead if the roleplay and the scene call for it). If the prey fails they gain the Enthralled condition. While prey is Enthralled, grapple and vore checks against them automatically succeed, and they cannot take an Escape action. Each round where digestion damage occurs, the prey can make a will save against a DC of 10 + (1/2*predator's level) + (the higher of “number of predator feats” and CHA) to remove the Enthralled condition. The DC reduces by 1 each time the prey fails a check. Once the prey succeeds on a save, they cannot become Enthralled by the same predator for 24 hours.
Once a prey is inside a predator's body, the predator has several options to deal with them. Each turn, the predator makes a fresh vore check against their prey's CMD (without the +5 bonus for controlling the grapple). If the predator succeeds, they may choose to Digest, Pin, or Spit Out their prey. If the predator does not succeed, the prey is not automatically freed; instead, the predator cannot act against the prey, and on the prey's next turn they receive a +5 bonus to attempts to escape the stomach. If there are multiple creatures in your body, you make one vore check and apply the result to all of them, and must also perform the same action on each creature if the check is successful. Each of these actions counts as a free action and may be taken at any point in the predator's turn, but only one such action can be performed on prey per round.
Digest: Once an opponent is fully swallowed, you can attempt to digest them on a successful vore check. You deal 1d6 points of bludgeoning damage plus your Strength modifier, plus an additional 1d6 points of acid damage plus your Constitution modifier. At 4th level and every four levels thereafter (8, 12, 16, 20) both increase by an additional 1d6.
Pin: The predator's body smothers the prey, holding them tight and helpless. The prey gains the pinned condition, but the predator does not take any penalties. Note that predators are considered able to pin indefinitely while they are conscious and out of combat.
Spit Out: Force all creatures out of your body. All swallowed creatures are released into the an adjacent square of the predator's choosing, and are no longer grappled or swallowed by you. Prey expelled in this way land prone unless they make a DC 15 acrobatics check. Most predators don't spit out their prey unless they need to remove the stuffed penalty, or if their prey is particularly good at upsetting their stomach.
A creature's capacity depends on its size, and defines how many prey it can comfortably fit inside its stomach. As a creature's capacity increases, so too does their strength and body in order to hold prey relatively unencumbered. A higher capacity also indicates a quicker digestion time, and also makes them require increasingly large amounts of food to sate their exponentially increasing metabolism. Certain creatures may have special traits that allow them to defy these rules, and certain spells may affect capacity.
A creature's Maximum Capacity is equal to twice its Capacity. A creature can attempt to devour a creature that would bring it past its maximum capacity if it can somehow reach it and successfully grapple it.
To calculate how full you are, add up the base size capacity (or Prey Capacity) of every creature currently in your stomach, and compare it to your own capacity. This includes creatures inside of creatures you have eaten.
For most creatures, how much capacity space they fill when swallowed is always equal to their base capacity value determined by their size. However, some creatures may have unusually large bodies, or otherwise fill up more space than normal. As such, this system also uses a second capacity value, which is calculated as such:
Prey Capacity Value = Base capacity from creatures size + special modifiers
Prey reduced to -HP in a combat do not count as dead but rather 'defeated' until combat is over, and that 'defeated' prey that are regurgitated or rescued during combat or immediately afterwards may be revived as though they were 1 HP from death. For the sake of roleplay digesting meals remain conscious for 1/4 the time it takes to digest the capacity before expiring. If spit out during this time they may still live yet and are considered to be in stable condition. Once your prey expires, you begin to digest its remains completely. At this point, digestion is no longer a matter of damage, and effects such as damage reduction and acid resistance or immunity no longer apply. Instead, the time to digest is based on the total capacity your meal takes up, as shown on the table below. The GM has final say as to the digestion time for extremely excessive meals, and may impose additional penalties at their discretion. Creatures that are dead but not fully digested count as one size category smaller for stuffing penalties.
Eating a foe isn't just a great way to clear a battlefield or a dungeon. It's also a handy snack!
When you finish digesting a creature (or multiple creatures), your physical needs for food are put on pause for a time as you are considered fed.
In addition, your days without eating are reset to 0, and do not begin to accumulate until a number of extra days. The amount of extra days you receive depends on your capacity as well as the amount you ate, and follows the guidelines set below:
If you've been swallowed or partially swallowed, you can still fight back against your attacker. You can attempt the following actions against your opponent while swallowed or partially swallowed.
Attack: You can attack your opponent's stomach with a light or natural weapon. The AC of a creature's interior is equal to 10 + any deflection, luck, morale, natural armor, profane, or sacred (not size) bonuses to AC. All damage applies to the predator's stomach, and if your opponent has any damage reduction or other special defenses, they also apply to the stomach. Once you've dealt damage equal to one-half of the swallower's maximum hit points, the swallower becomes nauseated and must attempt to use the Spit Out action the next chance they get. Only 1 attack can be made per round, no matter how many attacks/round a player normally gets from natural weapons or high base attack bonus.
Cast a Spell: You can attempt to cast spells from inside your opponent's stomach. To cast a spell inside a stomach, treat the swallowed condition as though you were being grappled and make a concentration check accordingly. Also, all stomachs have a spell resistance equal to 10 plus your opponent's Hit Dice. Failure means you lose the spell, and your opponent regains 1 hit point per level of the spell lost.
Escape: You can attempt to escape from a mouth or stomach as a standard action by making either a combat maneuver check or an Escape Artist check against your pred’s CMD. If your check is successful, you move from swallowed to partially swallowed, or partially swallowed to being free (not grappled).
Struggle/Massage: When all else fails, you can thrash around as violently as possible to upset your opponent's stomach or arouse them. This is considered a dirty trick in addition to a combat maneuver, so any modifier that applies to either maneuver applies to your check. If your check is successful, you can choose to either 'sicken' (this mechanical condition covers either intense pleasure or unhappiness) your opponent or double your size when determining stuffed penalties. Both effects last for 1 round.
Disabled, Helpless, Paralyzed, Petrified, and Unconscious: Creatures suffering from these conditions cannot effectively defend themselves, and may be entirely swallowed with a single standard action.
Sleeping: Sleeping targets may be completely swallowed with a standard action, but they receive a Perception check versus the predator’s vore check as a DC to notice the attempt. If successful, they awaken and are have the partially swallowed condition. If they fail that check, they remain sleeping inside the predator’s body. They receive another check with a +4 bonus if they are dealt digestion damage or undergo abrupt movement (such as the predator moving at over half speed), which increases by +2 for each subsequent round of digestion or heavy activity if they still remain asleep.
Digested: A digested creature is not only dead, its body has been broken down and absorbed by a predator. What little remains of a digested creature will still function for the purposes of a raise dead or resurrection spell, although securing them will likely be problematic. (The GM may at their discretion either accept the live predator or the prey's “remains” as valid materials for a spell requiring the deceased's body).
Nauseated: Being nauseated functions as described in the SRD, except as noted here. While nauseated, maintaining a grappled against swallowed creatures is a move action instead of a free action.
Stuffed: You ate too much. This applies when a character eats more than their size class, with two of any size class counting as 1 of a larger size class. (i.e. a medium character can eat a medium character without penalty, but would be stuffed if they ate a large character, or a medium and a small character at the same time). You take a -10 foot penalty to all forms of movement. AC and CMD for all purposes except vore checks receive a -4 penalty, as do all attack rolls or CMB checks other than vore checks.
Extremely Stuffed: You ate way too much. This applies when a character eats more than what would Stuff a creature one size class larger. That is, a medium character consumes a number of prey equal to more than double their capacity by default to be Extremely Stuffed. The predator's movement speed drops to 5' per round and doubles the AC/attack penalties given in Stuffed.
Swallowed (partial): You're inside another creature's mouth (or a similar orifice). This condition supersedes 'grappled'. You're considered flat-footed against bite attacks made by the target grappling you. A successful combat maneuver check or Escape Artist check eliminates the swallowed condition.
Swallowed: You're inside another creature's stomach (or a similar digestive organ). This condition supersedes 'grappled'. Your opponent can move you without making a grapple check. Swallowed characters can only attack or be attacked by each other, or the stomach itself. Invisibility grants no benefit against the creature who swallowed you. A successful combat maneuver check or Escape Artist check changes your condition to swallowed (partial).