Updated.
Revising Antaeus...
Antaeus
Large Giant
Hit Dice: 32d8+254 (398 hp)
Initiative: +0
Speed: 40 ft. (8 squares)
Armor Class: 24 (-1 size, +15 natural), touch 9, flat-footed 24
Base Attack/Grapple: +24/+53
Attack: Slam +35 melee (1d8+11/19-20) or rock +24 ranged (2d6+11)
Full Attack: 2 slams +35 melee (1d8+11/19-20) or rock +24 ranged (2d6+11)
Space/Reach: 10 ft./10 ft.
Special Attacks: Rock throwing
Special Qualities: Low-light vision, resistance to acid 5, rock catching, specialized powers (earth mastery, great wrestler, growth, instantaneous healing)
Saves: Fort +24, Ref +10, Will +14
Abilities: Str 32, Dex 10, Con 24, Int 8, Wis 11, Cha 12
Skills: 33
Feats: Awesome Blow, Cleave, Endurance, Epic Toughness, Epic Will, Great Cleave, Improved Bull Rush, Improved Critical (slam), Improved Grapple (B), Improved Sunder, Legendary Wrestler (B), Power Attack, Weapon Focus (slam)
Environment: Any
Organization: Solitary
Challenge Rating: 21
Treasure: Standard
Alignment: Usually chaotic evil
Advancement: 31-34 HD (Large) or by character class
Level Adjustment: —
Earth Mastery (Ex): The gigantes gains a +1 bonus on attack and damage rolls if both it and its foe are touching the ground. If an opponent is airborne or waterborne, the gigantes takes a –4 penalty on attack and damage rolls.
Great Wrestler: The gigantes gains Improved Grapple and Legendary Wrestler as bonus feats.
Growth (Su): As long as it is in contact with the ground, the gigantes may, as a free action, begin growing, increasing his mass and physical prowess incrementally. So long as it wishes and remains in contact with the ground, the gigantes will continue to grow every subsequent round, at the beginning of its turn. When the gigantes grows, its size increases to the next highest size category, gaining all benefits and penalties for the size increase (ability scores, natural armor bonus, and base slam damage change appropriately), and doubling in height and weight. When the gigantes reaches Colossal size it stops growing, but can remain at that size as long as it wishes.
When the gigantes wishes to end this ability, loses contact with the ground, becomes unconscious, or dies, it returns to its normal size by decreasing to the next lowest size category each round.
Instantaneous Healing (Ex): If the gigantes begins its turn in contact with the earth, it instantly regains all lost hit points. This works just like natural healing. It does not restore hit points lost from starvation, thirst, or suffocation, and it does not allow the gigantes to regrow or reattach lost body parts.
Feel free to recommend feat replacements.