Summon the wrong demon? Call an angel by mistake? What are the things that can go wrong when you are performing summoning or calling spells or rituals?

Billions of randomly generated diseases.

One hundred fears and phobias that your players may get during their travels!

One hundred things that your players find missing after waking up from sleep.

One hundred different things that a Demon or Devil would want from your adventurers in exchange for some help.

One hundred different dark gifts that always come with a price...

One hundred different side effects from spending too much time in the Shadowfell.

One hundred horrible diseases that your players HOPEFULLY don't catch!

One hundred and twelve different hallucinations your players might experience while adventuring... or eating something they shouldn't.

I hope you cast the teleportation spell right!

What happens after you reach zero HP? How bad was that final blow?

One hundred things that can go wrong (or right) when casting a spell!

One hundred different ways you can recharge that magic item of yours!

You can speak 3 additional languages, chosen by the DM, for 1d10 days. Roll on the polymorph table. You can jump four times as high for 24 hours, also all fall damage you take is divided by four for the duration. Your WIS increases by…

The afflicted thinks every other creature is more powerful than it, and treats them with either respect or fear. The afflicted thinks its power became overwhelming, and hardly ever attacks out of fear of breaking the world. You realize…

This would be for a location (a spring) that grants a random 24 hr boon to a player that interacts with it in the approriate manner (like bathing in it or drinking from it). Alternatively, this can simply serve as inspiration for a spring…

Grow considerable body hair for 1 minute. Grow considerable body hair for 10 minutes. Grow considerable body hair for 1 hour. Grow considerable body hair for 1 day. Grow considerable body hair for 1 year. Heals 1 hp when eaten.…

The character no longer has a shadow. The character has forgotten their own name. No one will remember them, even close friends and family. Every time you sleep, you only dream of yourself lying awake and wake up less rested than…

While dead, the character kept having the feeling of drowning. When brought back, the character is forever scared to death by water. You suddenly speak and read a random language (possibly DMs choice) and have lost the ability to speak…

The character cannot turn right until the curse is lifted. Characters feet always sink at least 1 inch into any surface they walk on (the at least accounts for walking on water, as in if they try to walk on water they sink normally)…