If you want to make your campaign more like Myth (which was the actual premise of the LotFP campaign I'm running now), roll on the following table for something to add to your next adventure, or just pick something that fits.
1. A whole bunch of undead monsters. No, more than that. Enough that the players will need to either flee or enlist a small army to help them fight. And have the undead be an organized fighting force, not just a series of short encounters.
2. Dwarves with bombs. Bonus points for friendly fire.
3. Arrows made out of the bones of the severed limb of an evil wizard. If you shoot that wizard with them, the wizard turns to stone.
4. Scantily-clad folks waving around greatswords and painting themselves blue.
5. Magic roots that heal people. Bonus points if someone repurposes a root-digging shovel as a weapon.
6. Bloated undead that explode like TNT if they take more than a tiny bit of damage. Their bits and pieces act as shrapnel that paralyze those they hit. They carry around daggers so they can detonate themselves.
7. Undead monsters hiding underwater in ambush. Bonus points if they taint the water supply.
8. A book that can tell you anything from the past or future, but you can only open it to a random page and have no control over what it actually lets you read.
9. A pocket dimension full of spiders and pyramids of severed heads. Bonus points for M. C. Escher references.
10. Giants that can kill the average human with a single kick, but that turn to stone when they take too much damage.
11. Desperate villagers fleeing in droves to one of the few remaining safe places. They won't be safe for long.
12. People who are very talented at fighting, but handicap themselves by wearing heavy tiles from the walls of a distant palace as penance.
13. A spell that blows up a whole crowd of people/monsters in an impressive chain reaction, provided the targets stand close enough together. Theoretically, if everyone in the world were to line up closely and refuse to move, one casting of the spell would kill them all.
14. Monsters that used to terrorize the entire human population have now gone extinct themselves, but eventually they somehow come back to life.
15. A wizard who dives to the floor of the ocean to learn forbidden magical secrets.
16. A bottomless pit. Everyone knows it's there, but they generally ignore it. If you throw in a certain object, an explosion emanates from the pit.
17. A Dream Duel between wizards, as psychological as it is supernatural.
18. A giant stone head worshiped by nomadic ape-like creatures. They roll the head along with them as they migrate. Bonus points if someone wants to blow it up.
19. A wizard frozen in a river or buried in a landslide, but not dead.
20. Forest giants that promise to come help you out, but don't show up. Assholes.
21. People who dual-wield katanas and reference non-European animals like jaguars in an otherwise Medieval Europe-flavored setting.
22. Two groups (bonus points for whole armies) of undead fighting each other, with innocent people caught in the crossfire.
23. A small number of heroes defend a narrow mountain pass from a much larger force. Bonus points for a rain of arrows that blots out the sun.
24. Ancient stone monuments that are secretly part of a teleportation network. Bonus points if someone wants to blow them up to keep someone else from using them.
25. A bow that shoots lightning, a sword that shoots lightning, and undead monsters that shoot lightning.
26. Monsters from another dimension that are trapped in the players' world. They must wear the skins of native creatures so that the local god does not see and smite them. Because of this, no one in this world knows what they actually look like.
27. The number 7, which keeps popping up again and again. You feel as if you remember it from a dream, but you can't quite remember...
28. Huge cities made of iron, now melted and warped, buried in the wasteland. The rivers run red with rust.
29. Cultists, warlocks, bandits, or other dumbasses who collaborate with the forces of darkness even though said forces of darkness clearly intend to betray them and drive their species to extinction.
30. A spell that turns the caster into a flock of ravens. If you kill one of the ravens, the caster can never cast the spell again once they return to their normal form, and they become even crazier than usual.