So You Touched the Glyph of Monsters...

Similar to the traditional glyph of warding (if arguably much more irresponsible), the glyph of monsters spell was discovered on a prehuman stele by the late sorcerer Galgolus of Ixmere and subsequently transcribed by his sole surviving apprentice (who had been out sick that day).

d12
1. Puny humanoids erupt from thin air in a continuous stream, armed to the teeth, drunk with battle-lust, continue to appear until numbers exhausted (10d12 total), if victorious they maintain a perpetual vigil over the inscribed object to the extent of their lifespans, set up for long term habitation, assert selves as new dungeon faction
2. Inscribed object transmutes into alligator size reptilian shape w/giant mouth: hisses, lashes tail as warning display, if unheeded lunges w/jaws agape then flesh-rending death roll, reverts to original form when everyone is either gone or dead
3. Dimensional portal explodes into view, swirling Steve Ditko space beyond, giant invisible pudding oozes through to dissolve all that lives near, then moves on to terrorize the surrounding area
4. Millions of venomous spiders materialize around inscribed object, settle into form of single giant spider, very hard to kill by traditional means, gets progressively smaller as constituent parts destroyed, each time it hits scads of individual spiders go scrambling all over target, getting under armor, biting like hell
5. Tapeworm of the Gods surges through manhole sized portal, violently, speedily draining the juice from any hit, disappears when present company dispersed
6. Ogre-sized, roughly human shape of earth & stone bursts from nearest surface, issues withering verbal abuse to all within range, preternaturally aware of foibles, personal failings, after thorough dressing-down, pummels all with massive fists until satisfied inscribed object secure, then crumbles into heap
7. Jet black giant ape appears in smoky flash: seizes, rends humans limb from limb w/giant hands, incredible strength, applies lethal pro wrestling moves to any who stick around, terminates self with sleeper hold upon victory
8. Levitating blob w/tentacle array arrives via localized reality-breach, large central semi-sympathetic human-like eye, radiates crackling electricity 10' radius, semi-accurate lightning bolts from eye fly about willy-nilly, levitation glands in body cavity may be harvested, deflates in 30 minutes
9. Sudden explosive fungal bloom fills 10' cube, smothering anyone within range, abruptly takes on shape of giant bear w/scimitar-sized claws, deals w/survivors then lies down and festers
10. Powerful demon with excellent manners emerges from gate to talk things over and/or kill everyone present, then seeks out original caster for light torture, stern talking to
11. Following a rainbow explosion, anthropoid embodiment of excellent prismatic spray steps forth accompanied, inexplicably, by thunderous syncopated drumming, emits lethal bands of light from each graceful jazz hands-like gesture, can only damage itself via mirrors, initiates random reign of terror if victorious
12. Whosoever touches the glyph becomes a monster (see subtable, below)

So You Became a Monster...
d6
1. Mouth transmutes into that of great white shark, eyes become lifeless, like a doll's eyes, singular urge: bite everyone to death
2. Outer husk splits, sloughs off, human-shaped jelly of remarkable speed leaps upon nearest living target for suffocation/digestion, caustic bile spews from mouth hole in constant fountain
3. Grow to 17' tall, commensurate strength, involuntary huge beaming/crazy smile, emit nonstop terrible giggling, pick up those nearby, chew on heads
4. Skin becomes nearly impervious blue chitin, tongue grows into spring-loaded spear supplied w/ lethal venom by huge unsightly glands in neck
5. Nervous system leaps from body (which crumples into lifeless heap), dances around wildly, delivers potent dose of electricity on contact, able to extend self indefinitely in many directions at once
6. Muscles instantly swell to absurd proportions, head shrinks down to tiny nub, beats the hell out of all and sundry while screaming threats/obscenities in high pitched version of original voice

Notes: In each case the former PC viciously attacks all within range, monstrous condition permanent until reversed by a successful dispel magic