The question is edition-less, but for the record it's for a party of about five 11th-12th level PCs in 5e.
How can I spice up this encounter with a chimera? It feels oddly out-of-place and underdone (not to mention underpowered for my party) in an otherwise wondrous dungeon.
Here's the original write-up:
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2. Guardian Room
[SECTION]Beyond the door is a 40' x 30' room with a copper door on the far side. The floor is a mosaic of red and yellow geometric patterns, and the bare rock wall are as smooth as marble.[/SECTION]
The floor is a magical trap. When anyone not wearing one of Nazir's rings of returning (see the sidebar on page 45) steps into the room, he or she triggers a create any monster spell that conjures a chimera in the center of the room. The chimera attacks for the duration of the spell (three turns) or until it is killed. It will not leave the room and does not have enough room to fly.
The chimera cannot strike PCs protected by anti-magic shells or protection from evil spells, although PCs protected by the latter are still subject to its ranged attack (breath weapon). The chimera reappears each time the PCs reenter this room, but it does not regain lost hit points automatically. Once the chimera is slain, Nazir must recast his spell to prepare another guardian for this chamber.
The copper door on the far side of the room is unlocked and opens onto a set of steps that rises to area 3.
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I have some ideas involving a swirling pattern on the floor empowering the chimera if it's stepped on in the wrong order / out-of-sequence. But I'd love to hear any ideas you have 
Further details and picture of intro...
[SBLOCK=In spoilers because we're running this game on ENWorld and I don't want players seeing]
The adventure's premise is to free a princess who looks live a prince's beloved. The prince has charmed her and taken her captive; he's been polymorphed by a wicked mage and in the process went a little nuts. The mage polymorphed him because the prince was to elope with his daughter. Outraged at his daughter, the mage turned her into a statue. The PCs come in to rescue the princess originally, but end up on a quest to reunite prince & mage's daughter. I'm adding a few more layers in my own game, but that's the gist of the original.
The dungeon is the Fortress of Nazir al-Azrad, the hidden redoubt of a wicked mage in a desert mountain fissure. This room is literally the first room of the dungeon after wending through the fissure. The mage commands a magic called the White Flame, which is a bizarre heatless flame which heals/rejuvenates creatures entering it (and grants the mage immortality)...however it does this by transferring any damage/conditions to creatures imprisoned in the crystals that the flame causes to grow. This White Flame grants his mortal followers some damage resistances and they can use their rings of returning to teleport back to it to heal up. Remind me a bit of the AD&D Positive Energy Plane / Plane of Radiance.
EDIT: I've also created Nazir's spellbook, based on the spells listed for the NPC and on other spell effects described in the dungeon that he would have cast...
Nazir’s Spellbook
1st level: attract evil eye*, charm person, detect magic, false life, mage armor, magic missile
2nd level: arcane lock, continual flame, detect thoughts, mirror image, see invisibility, web
3rd level: dispel magic, fly, haste, hold person, sending, slow
4th level: confusion, dimension door, greater invisibility, hallucinatory terrain
5th level: geas, hold monster, telekinesis, teleportation circle, wall of stone
6th level: disintegrate, flesh to stone, magic jar
7th level: force cage, teleport
8th level: dominate monster, power word stun
9th level: true polymorph
[/SBLOCK]
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