It wouldn't be that hard, really. For instance...
Varanthian, female half-fiend behir (CL 10)
LE huge outsider (native) 9
Init +3; Senses Perception +16, low-light vision, scent
DR 5/magic; Acid 10, cold 10, fire 10
Immune electricity, poison
Languages Known Common, Draconic, Infernal
Defenses Ref 23*, Fort 22*, Will 15*
*+10 against spells
hp 103; Threshold 32
Speed 8 squares, climb 3 squares, fly 8 squares
Melee bite +17 (2d6+10) plus grab and 2 claws +12 (d8+5)
Ranged breath weapon +10 (7d6 electricity, line, 1/10 rounds)
Fighting Space 3 squares x 3 squares; Reach 2 squares
Base Atk +9; Grp +27
Abilities Str 30/+10, Dex 17/+3, Con 23/+6, Int 11/+0, Wis 14/+2, Cha 14/+2
Feats Alertness, Cleave, Power Attack, Track
Skills Acrobatics +9, Climb +30, Jump +16, Perception +16, Perform +8, Stealth +7, Survival +14 (+16 to follow tracks)
Spell Resistance Varanthian gets +10 to all defenses against spells.
Spell-Like Abilities 3/day: darkness, poison (+17 melee vs. Fort, Treat Injury DC 16); 1/day: contagion (+5 vs. Fort, Treat Injury DC 15), desecrate, unholy blight (+6 vs. Will)
Smite Good Once per day, Varanthian may do +9 damage with her first attack in a round against a character of any good alignment. If the attack misses, the smite is lost.
Constrict Varanthian deals 2d8+10 with a successful grapple check. She can make six rake attacks (+15 melee, d8+5 damage) against a grappled foe as well.
Improved Grab If Varanthian hits a target with her bite attack, she may initiate a grapple with that target as a reaction without provoking an attack of opportunity.
Swallow Whole Varanthian can attempt to swallow a grabbed creature of medium or smaller size as a standard action with a successful grapple check. If she swallows the opponent, she can use Cleave to try to bite and grab another opponent. A swallowed creature takes 2d8+10 plus 8 acid damage each round and can cut its way out by using a light slashing or piercing weapon to deal 25 points of damage to the gizzard (Ref defense 15). Varanthian's gizzard can hold 2 medium or 8 small opponents.
Of course, doing that would require the PCs to be Saga-ized too, which is actually the tougher prospect — mainly because their classes and spells would require converting. I expect it wouldn't be worth the effort … but it's kinda fun to think about.