How about a wine barrel (or two) getting punctured. At first, it provides a moment of comic relief as someone (perhaps a participant in the seance) takes a drink - after all, this was the last barrel of a particularly good vintage, so this will be the last chance in the entire world for anyone to get it. However, after a few rounds, when the floor is soaked in alcohol, it's a hazard just waiting for someone to cast a fire spell.
A second 'assassin' could be an entertaining gimmick. He's not really a fighter, just a nervous cat burglar trying to score some jink on the side by offing some rich lady for a lucrative client. He's been patiently hiding in the rafters all night long so that he can get a clean shot to drop something heavy on her, or shoot a poisoned dart into her neck or something. And of course, after each time he painstakingly manuvers into position for some silly attack, either she evades him completely by accident or gets pulled to safety by a dashing PC - or his attack is ruined by the action happening down below; for instance, a ninja using the table as a springboard to the rafters bumps the thief on his way up, making him drop his weapon and sending him sprawling into a precarious position.
Courtesy of thesaurus.com:
Entry: run
Function: verb
Definition: move fast
Synonyms: abscond, amble, barrel, beat it, bolt, bound, bustle, canter, career, clear out, course, dart, dash, decamp, depart, dog it, escape, flee, flit, fly, gallop, hasten, hie, hotfoot, hurry, hustle, jog, leg it, light out, lope, make off, make tracks, pace, race, rush, scamper, scoot, scorch, scramble, scud, scurry, shag, shoot, skedaddle, skip, skitter, smoke, speed, spring, sprint, spurt, take flight, take off, tear, tear out, travel, trot, whisk
Entry: jump
Function: verb
Definition: leap
Synonyms: bail out, barge, bob, bounce, bound, buck, canter, caper, clear, curvet, dive, drop, fall, gambol, hop, hurdle, hurtle, jerk, jiggle, jounce, lollop, lop, lunge, lurch, parachute, plummet, pop out, pop up, quiver, rattle, ricochet, saltate, shake, skip, sky, somersault, spring, surge, take, top, trip, vault, waver, wobble
Entry: dodge
Function: verb
Definition: avoid
Synonyms: circumlocute, dark, deceive, ditch, duck, elude, equivocate, escape, evade, fence, fend off, fudge, get around, hedge, juke, lurch, malinger, parry, pussyfoot, shake, shake off, shift, shirk, short-circuit, shuffle, sidestep, skirt, slide, slip, swerve, tergiversate, tergiverse, trick, turn aside, weasel
Entry: strike
Function: verb
Definition: hit hard
Synonyms: bang, bash, bean, beat, boff, bonk, box, buffet, bump into, chastise, clash, clip, clobber, clout, collide, conk, crash, cuff, ding, drive, force, hammer, impel, knock, nail, percuss, plant, pop, pound, pummel, punch, punish, run into, slap, slug, smack, smash into, sock, swat, thrust, thump, touch, wallop, whop