Just go the easy route 
TARRASQUE BUNNY
Diminutive Magical Beast
Hit Dice: 48d10+255 (519 hp)
Initiative: +12
Speed: 40 ft. (8 squares)
Armor Class: 42 (+4 size, +3 Dex, +25 natural), touch 17, flat-footed 39)
Base Attack/Grapple: +48/+34
Attack: Bite +60 melee (1d3-2/18–20/x3)
Full Attack: Bite +60 melee (1d3-2/18–20/x3) and 2 horns +55 melee (1d2-2) and 2 claws +55 melee (1d2-2) and tail slap +55 melee (1d3-2)
Space/Reach: 2.5 ft./ 0ft.
Special Attacks: Augmented critical, frightful presence, improved grab, rush, swallow whole
Special Qualities: Carapace, damage reduction 15/epic, immunity to fire, poison, disease, energy drain, and ability damage, regeneration 40, scent, spell resistance 32
Saves: Fort +38, Ref +29, Will +20
Abilities: Str 6, Dex 26, Con 18, Int 3, Wis 14, Cha 14
str-39, dex +10, con -17
Skills: Listen +17, Search +9, Spot +17, Survival +14 (+16 following tracks)
Feats: Alertness, Awesome Blow, Blind-Fight, Cleave, Combat Reflexes, Dodge, Great Cleave, Improved Bull Rush, Improved Initiative, Iron Will, Power Attack, Improved toughness, Toughness (5)
Environment: Any
Organization: Solitary
Challenge Rating: 15
Treasure: None
Alignment: Always neutral
Advancement: 49+ HD (Colossal)
Level Adjustment: —
The tarrasque bunny is 1 foot long and 1.5 feet tall, and it weighs about 1 ton.
The tarrasque cannot speak.
COMBAT
The tarrasque bunny attacks with its claws, teeth, horns, and tail.
The tarrasque bunnies natural weapons are treated as epic weapons for the purpose of overcoming damage reduction.
Augmented Critical (Ex): The tarrasque bunnies bite threatens a critical hit on a natural attack roll of 18–20, dealing triple damage on a successful critical hit.
Frightful Presence (Su): The tarrasque bunny can inspire terror by charging or attacking. Affected creatures must succeed on a DC 36 Will save or become shaken, remaining in that condition as long as they remain with 60 feet of the tarrasque bunny. The save DC is Charisma-based.
Improved Grab (Ex): To use this ability, the tarrasque bunny must hit a medium or smaller opponent with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can try to swallow the foe the following round.
Rush (Ex): Once per minute, the normally slow-moving tarrasque bunny can move at a speed of 200 feet.
Swallow Whole (Ex): The tarrasque bunny can try to swallow a grabbed opponent of diminutive or smaller size by making a successful grapple check. Once inside, the opponent takes 1d8 points of crushing damage plus 1d4 points of acid damage per round from the tarrasque bunnies digestive juices. A swallowed creature can cut its way out by dealing 8 points of damage to the tarrasque bunnies digestive tract (AC 25). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out. The tarrasque bunnies gullet can hold 2 Tiny or smaller creatures.
Carapace (Ex): The tarrasque bunnies armorlike carapace is exceptionally tough and highly reflective, deflecting all rays, lines, cones, and even magic missile spells. There is a 30% chance of reflecting any such effect back at the caster; otherwise, it is merely negated. Check for reflection before rolling to overcome the creature’s spell resistance.
Regeneration (Ex): No form of attack deals lethal damage to the tarrasque. The tarrasque bunny regenerates even if it fails a saving throw against a disintegrate spell or a death effect. If the tarrasque bunny fails its save against a spell or effect that would kill it instantly (such as those mentioned above), the spell or effect instead deals nonlethal damage equal to the creature’s full normal hit points +10 (or 519 hp). The tarrasque bunny is immune to effects that produce incurable or bleeding wounds, such as mummy rot, a sword with the wounding special ability, or a clay golem’s cursed wound ability.
The tarrasque bunny can be slain only by raising its nonlethal damage total to its full normal hit points +10 (or 519 hit points) and using a wish or miracle spell to keep it dead.
If the tarrasque bunny loses a limb or body part, the lost portion regrows in 1d6 minutes (the detached piece dies and decays normally). The creature can reattach the severed member instantly by holding it to the stump.
Skills: The tarrasque bunny has a +8 racial bonus on Listen and Spot checks.
Diminutive Magical Beast
Hit Dice: 48d10+255 (519 hp)
Initiative: +12
Speed: 40 ft. (8 squares)
Armor Class: 42 (+4 size, +3 Dex, +25 natural), touch 17, flat-footed 39)
Base Attack/Grapple: +48/+34
Attack: Bite +60 melee (1d3-2/18–20/x3)
Full Attack: Bite +60 melee (1d3-2/18–20/x3) and 2 horns +55 melee (1d2-2) and 2 claws +55 melee (1d2-2) and tail slap +55 melee (1d3-2)
Space/Reach: 2.5 ft./ 0ft.
Special Attacks: Augmented critical, frightful presence, improved grab, rush, swallow whole
Special Qualities: Carapace, damage reduction 15/epic, immunity to fire, poison, disease, energy drain, and ability damage, regeneration 40, scent, spell resistance 32
Saves: Fort +38, Ref +29, Will +20
Abilities: Str 6, Dex 26, Con 18, Int 3, Wis 14, Cha 14
str-39, dex +10, con -17
Skills: Listen +17, Search +9, Spot +17, Survival +14 (+16 following tracks)
Feats: Alertness, Awesome Blow, Blind-Fight, Cleave, Combat Reflexes, Dodge, Great Cleave, Improved Bull Rush, Improved Initiative, Iron Will, Power Attack, Improved toughness, Toughness (5)
Environment: Any
Organization: Solitary
Challenge Rating: 15
Treasure: None
Alignment: Always neutral
Advancement: 49+ HD (Colossal)
Level Adjustment: —
The tarrasque bunny is 1 foot long and 1.5 feet tall, and it weighs about 1 ton.
The tarrasque cannot speak.
COMBAT
The tarrasque bunny attacks with its claws, teeth, horns, and tail.
The tarrasque bunnies natural weapons are treated as epic weapons for the purpose of overcoming damage reduction.
Augmented Critical (Ex): The tarrasque bunnies bite threatens a critical hit on a natural attack roll of 18–20, dealing triple damage on a successful critical hit.
Frightful Presence (Su): The tarrasque bunny can inspire terror by charging or attacking. Affected creatures must succeed on a DC 36 Will save or become shaken, remaining in that condition as long as they remain with 60 feet of the tarrasque bunny. The save DC is Charisma-based.
Improved Grab (Ex): To use this ability, the tarrasque bunny must hit a medium or smaller opponent with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can try to swallow the foe the following round.
Rush (Ex): Once per minute, the normally slow-moving tarrasque bunny can move at a speed of 200 feet.
Swallow Whole (Ex): The tarrasque bunny can try to swallow a grabbed opponent of diminutive or smaller size by making a successful grapple check. Once inside, the opponent takes 1d8 points of crushing damage plus 1d4 points of acid damage per round from the tarrasque bunnies digestive juices. A swallowed creature can cut its way out by dealing 8 points of damage to the tarrasque bunnies digestive tract (AC 25). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out. The tarrasque bunnies gullet can hold 2 Tiny or smaller creatures.
Carapace (Ex): The tarrasque bunnies armorlike carapace is exceptionally tough and highly reflective, deflecting all rays, lines, cones, and even magic missile spells. There is a 30% chance of reflecting any such effect back at the caster; otherwise, it is merely negated. Check for reflection before rolling to overcome the creature’s spell resistance.
Regeneration (Ex): No form of attack deals lethal damage to the tarrasque. The tarrasque bunny regenerates even if it fails a saving throw against a disintegrate spell or a death effect. If the tarrasque bunny fails its save against a spell or effect that would kill it instantly (such as those mentioned above), the spell or effect instead deals nonlethal damage equal to the creature’s full normal hit points +10 (or 519 hp). The tarrasque bunny is immune to effects that produce incurable or bleeding wounds, such as mummy rot, a sword with the wounding special ability, or a clay golem’s cursed wound ability.
The tarrasque bunny can be slain only by raising its nonlethal damage total to its full normal hit points +10 (or 519 hit points) and using a wish or miracle spell to keep it dead.
If the tarrasque bunny loses a limb or body part, the lost portion regrows in 1d6 minutes (the detached piece dies and decays normally). The creature can reattach the severed member instantly by holding it to the stump.
Skills: The tarrasque bunny has a +8 racial bonus on Listen and Spot checks.
*rushes off to put together a warforged rabbit for Eberron game*
