u/EndOk359

I was browsing the wiki after rewatching the episode where Rimuru goes to the labyrinth for the first time and I saw that to become a hero egg you need to have a contract with a light/dark elemental. Does this elemental have to be a Greater Elemental or can it also be an Elemental Lord?

Also, how strong is an Elemental Lord? The wiki says they are equivalent to Demon Lords and have the ability to manipulate spiritrons.