environmental damage is the answer here.

Have your DM introduce a storyline that starts off with interrograting drug dealers on roof tops.

The OneDND version of EK has this at level 7 now as well

He is Vigo! You are like the buzzing of flies to him!

Anus Tart, very nice

They sound like twats

Oh no, it’s salt water!

Keep in mind that just because the item is legendary doesn’t mean that they get to keep it. After it has served it’s purpose it could be destroyed or if they do get to keep it then it could be severely weakened or damaged, or it could even be something that isn’t meant for them.

This gives you some freedom to go absolutely bonkers with it since it’s only going to be used for a little bit.

A Giant Mecha to fight a Kaiju.

A dying god needs a new body.

A Mastersword like weapon

Are the Warforged a thing in your world? They could literally be the father of an entire race.

My personal favorite idea, assuming they’re into it. Let them design their own creation, they are the inventor after all.

There’s more than 1 way to become a sorcerer