Chimeric Ankheg* (CR 9)

Large Magical Beast
Alignment: Always chaotic evil
Initiative: +0; Senses: darkvision 60 ft., low-light vision, scent, tremorsense, Listen +8, and Spot +5

AC: 24 (-1 size, +15 natural), touch 9, flat-footed 24
Hit Dice: 9d10+45 (94 hp)
Fort +11, Ref +6, Will +4
Speed: 30 ft., burrow 20 ft., fly 50 ft. (poor)
Space: 10 ft./5 ft.
Base Attack +9; Grapple +20
Attack: Bite +12 melee and bite +10 melee and butt +10 melee
Full Attack: Bite +12 melee and bite +10 melee and butt +10 melee
Damage: Bite 2d6+7 (ankheg), bite 2d6+3 (dragon), butt 1d8+3
Special Attacks/Actions: Acid, breath weapon, improved grab, spit acid
Abilities: Str 25, Dex 11, Con 21, Int 3, Wis 13, Cha 6
Special Qualities:
Feats: Alertness; Toughness; Multiattack
Skills: Climb +8, Listen +8, and Spot +5
Advancement: 10-18 HD (Large); 19-27 HD (Huge)
Climate/Terrain: Temperate and warm forest, plains, and underground
Organization: Solitary, pair, or cluster (3-4)
Treasure/Possessions: None

Source: Monster Manual II

Here is a sample chimeric creature using an ankheg as the base creature and a white dragon head.

Acid (Ex): Acidic enzymes drip from the mouth of the ankheg head each round it maintains a hold on a grabbed creature. The acid automatically deals 1d4 points of acid damage each round.

Breath Weapon (Su): A chimeric ankheg's dragon head can emit a 20-foot cone of cold that deals 3d8 points of cold damage (Reflex DC 19 half).

Improved Grab (Ex): If a chimeric ankheg hits an opponent that is at least one size category smaller than itself with its ankheg bite attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +17). if it gets a hold, it has the option to conduct the grapple normally, or simply use its jaws to hold the opponent (-20 penalty on grapple check, but the chimeric ankheg is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals bite and acid damage. If the chimeric ankheg is damaged after grabbing its prey, it retreats backward down its tunnel at its burrow speed, dragging the victim with it.

Scent (Ex): A chimeric ankheg can detect approaching enemies, sniff out hidden foes, and track by sense of smell.

Spit Acid (Ex): A chimeric ankheg can spit a line of acid 5 feet high, 5 feet wide, and 30 feet long. Any creature hit by this attack takes 4d4 points of acid damage (Reflex DC 19 half). One such attack depletes the chimeric ankheg's acid supply for 6 hours. It cannot spit acid or deal acid damage with its bite during this time. Chimeric ankhegs do not use this ability unless they are desperate or frustrated. They most often spit acid when reduced to fewer than half of their hit points or when they have not successfully grabbed an opponent.

Tremorsense (Ex): A chimeric ankheg can automatically sense the location of anything within 60 feet that is in contact with the ground.