What if casting magic changed (for a few hours or days depending on the strength of the spell) the colour of the skin of the spellcaster? It could lead sadly to a very racist world to rp in.
“ The heroes are travelling the great seas by ship. One night when the seas are calm and everything seems fine their vessel is eaten by a great whale. The end? No. They wake in the belly of the animal, it is like a great cave. Full of wrecked ships and strange things to be discovered. Will they make it out alive?”
“ A Druid Circle that's witnessed the polution and destruction of Mankind plans to wipe out every technological race, turning the world into a Nature Nightmare.”
“ Whilst exploring underground the PCs discover tube like tunnels stretching for miles, upon further inspection the strange tunnels seem to connect all major cities in the are, what is their purpose?”