For me, I have done even new abilities. One of them I made is Maxthin which will disable either damaging or status moves when a Pokémon makes contact to a target with that ability.
Variants of intimidate are easy as well. I had made two ones: Intimidoom aka lower special attack of every opponent when the Pokémon enters battle and another one named Intimilow and works like intimidate but lowers Speed instead.
Last but not least, you could make a variation of Download ability. I have made one named Netplay that ups user’s Defense or Special Defense depending on target’s powers.