Topiary Guardian, Triceritops (CR 13)

Huge Plant
Alignment: Always neutral
Initiative: +1 (Dex); Senses: low-light vision and tremorsense 90 ft.

AC: 18 (-2 size, +1 Dex, +9 natural), touch 9, flat-footed 17
Hit Dice: 20d8+120 (210 hp); DR: 10/slashing
Fort +18, Ref +7, Will +6
Speed: 30 ft.
Space: 15 ft./10 ft.
Base Attack +15; Grapple +34
Attack: Gore +24 melee (4d6+16 or Powerful Charge 7d6+16)
Full Attack: Gore +24 melee (4d6+16)
Damage: -
Special Attacks/Actions: Merciful, trample 4d6+16
Abilities: Str 33, Dex 12, Con 22, Int -, Wis 10, Cha 1
Special Qualities: freeze, plant traits, vulnerability to fire
Feats: Powerful Charge
Skills: Move Silently +9
Advancement: -
Climate/Terrain: Any
Organization: Solitary or garden (2-8)
Treasure: None

Source: Monster Manual III

This neatly trimmed shrub has been impeccably sculpted into the shape of an triceritops.

A topiary guardian is a shrub or bush sculpted into the shape of an animal and then animated by arcane magic. As much decoration as defense, these creatures guard the courtyards of kings and nobles, blending in seamlessly among ordinary hedge sculptures. The guardians spring to life only when an intruder enters the garden.

Topiary guardians are as much construct as plant. They are not naturally mobile plant creatures; like golems, their animating force is a spirit from the Elemental Plane of Earth that has been bound to the body via magic. As a result, druids find them distasteful at best, and an abomination at worst. The wealthy landowners who keep the creatures in their gardens rarely worry about such issues, however. They consider the extra security of having a topiary guardian patiently waiting to spring on thieves or assassins more important than the shrub's "feelings." A topiary guardian is the same size as the creature it imitates, so a lion topiary guardian would have a lion's dimensions. However, a guardian is composed mostly of tiny branches and leaves, making it much lighter than a flesh-and-blood creature of the same size; it weighs only one-quarter as much as its flesh-and-blood counterpart. Topiary guardians do not speak, but do rustle slightly as they move.

A triceratops topiary guardian measures 25 feet long and weighs 5,000 pounds.