Agreed on the danger aspect… I don’t mind life-ending risk if there is life-enhancing reward. I keep thinking about an anomaly that animates plants and trees in its range…
Maybe an event that takes control of your character for a certain amount of turns, with different intents involved probably ranging between strange to downright harmful (rarely it’d be lethal, like losing control of yourself right after activating a grenade). Killing sprees, stripping clothing and throwing random items, attempting to consume every consumable in the inventory, shouting at the top of your lungs, rampaging against inanimate objects, self inflicted (potentially lethal?) injury, starting fires, I guess the possibility is endless… Cutting all cloth into rags, disassembling everything, grabbing every item in sight, opening all doors in sight, eating nearby corpses, dropping items or digging holes in patterns, ETC! ETC is the big one…
An anomaly that turns zombies into NPCs… One that destroys all buildings in a radius… I’d like to see snakes made out of fiery 4’s swimming around
Decent storyline-ish event could be an NPC from the future (or a parallel dimension), maybe to give you a futuristic edge or… possibly to take your eyeball-meat because the future is lacking in eyeball-meat
An event that duplicates all nearby inanimate objects one square to their right (this would make buildings have double-thickness walls on the east and west sides, plus double windows… it could also be applied seven or eight times (duplicated to the right) to make strange smeared areas). Earthquakes and tornados are good, anomalous or not. A strange being of energy issues forth and halves one stat (or skill) while doubling another. An anomaly that turns all present water into fire, or all liquids into something else (blood, acid, vomit, gasoline, because I know I’d like to light a river of gas, or swim in a river of jelly. An anomaly could change seasons, or day to night. Fill nearby houses with water (or acid, or vomit, or blood). Mentioned animated trees up top, but fighting a herd of toilets and refrigerators and cabinets would be good too… A rift that vomits up creepy items like fetuses or scalpels or human flesh… A rift that spawns a naked, weak, and brainless clone of you. An odd creature offers you the object of your wildest dreams (and has a 50/50 shot of simply giving you what you wished for, or giving basically a cursed version, where food poisons and weapons attack you and clothing clings to you and has to be worn to shreds to be removed).
Or one that births a Dwarf Fortress-ish randomized mutant horror, ranging between absolutely defenseless or too deformed to function, up to acid-breathing winged spike-encrusted murder machines.
(From the rift comes a (insert random color)-skinned
descriptor (gigantic, armless, legless, metallic, eyeless, skinless, formless,etc)
----like (ratlike, amphibian, skeletal).
It is totally (void of or encrusted) with (spines/flowers/eyeballs/teeth),
and its (harmless or dangerous) claws/fangs/tentacles/discharge is (toxic/paralytic/without effect).
Its ----- look(s) terribly effective. (muscles, bulging brain, aerodynamic nature, keen eyes, sharp claws)…
That’s getting difficult and confusing all at the same time 
It’d maybe be easier just to closely simulate the Dwarf Fortress beast generator, just with more useless creature features. Either way, you’d get results like:
From the rift squirms an emerald-colored serpentine creature. It is eyeless and its skeletal body is totally crusted in long spines. Its blunt fangs look terribly effective, while its milky eyes seem useless. The creature appears docile but may have capacity for violence. Occasionally it releases a high-pitched wail.
Where serpentine would have a bonus, say +5hp while something stronger like skeletal would get +20hp (or whatever is challenging, anyway). Eyeless could be -2 perception and -75% chance to hit. Crusted in long spines +5damage/+4defense. Blunt fangs +2damage +2blunt.
“look terribly effective” would apply a bonus to whatever it refers to in the description, which would turn +2dam +2blunt fangs into +3dam +3blunt fangs, and something like “looks useless” or “are thin and weak-looking.” would deduct from whatever its applied to… And here my own example creation bumps into a problem because its both eyeless and also has milky eyes
Can’t have both! Anyway, “creature seems docile” would mean it is a neutral creature and won’t attack unless provoked. “may have capacity for violence” would appear when it has body parts capable of attack (some formless blob would have something like “The creature seems thoughtless, and has no means of defending itself.”). “Occasionally it releases a high-pitched wail.” speaks for itself, I guess
Any of the character possession things I gave above work here, too. “It looks around ravenously, intent on eating.” “It begins to mindlessly rampage!” “The pitiful creature constantly injures itself.”. “The creature begins to dig holes.” “The curious creature seems intent on exploring.” “This creature glows bright, and begins to burn its surroundings!” (a lot of these would need legs to move with as a prereq)…
snaps out of it Ahem! In summarization, randomly spawned enemies are cool, especially when they can be mottled-grey tumors crusted in useless hands that cries like a human being (+20 dexterity for being crusted with hands!)… Or a humanoid stone-man that discharges gunpowder and fire 
I shall end all my posts with apologies, for spam, and for my incoherent wishlisting 