Hydra heads may be attacked directly as normal instead of making a sunder attempt. They take damage as normal and are severed or crushed when they reach 0 hp. They have the same AC as the hydra's body with a +2 bonus due to the size difference.
The heads do not count as separate creatures and so Cleave does not grant bonus attacks if a head is severed.
"Target" spells may target heads as though they were creatures.
Area of Effect spells affect the hydra as follows. Half of the spells damage (rounded up) is dealt to the creature's body, the remainder affects the creature's heads. The damage dealt to the heads is divided evenly among all heads, with any remainder being applied to the body.
For example, a Fireball deals a ten-headed hydra 26 damage and it fails it's Reflex save. 13 damage is applied to the body, the other 13 is applied to the heads. Each takes 1 point of damage, the remaining 3 is applied to the body. (for a total of 16) If the creature had passed it's save and taken half damage, the body would have taken 7 and the heads 6. Since 6 damage cant be applied to all 10 heads, it is added to the body's damage. The body takes 13, the heads take none.
A hydra takes up a "huge" (15'x15') square. The heads are medium sized and take up the squares around the hydra, as shown below. The heads have no reach from this location and may only attack to the front or the sides.
The hydra takes up all of the squares in red. The heads line up in the yellow squares. They may attack any of the blue squares.
The Paladin moves in to attack the Hydra's heads. He suffers no Attacks of Opportunity making this move. He may attack any of the three heads adjacent to him. He may only be attacked by the same three adjacent heads. He cannot attack the body unless he has a reach weapon.
The Paladin steps forward again. He suffers no Attack's of Opportunity because it was only a 5ft step. If he moved here from more than 10 ft away, he would have suffered attacks of opportunity from the three heads he passes. One head moves back to occupy one of the same squares as the body. In this position the Paladin may attack the body or any of the four adjacent heads. Any of those four heads may attack the Paladin.
