In most situations, I would go for Bold nature (+Def, -Attack) because of Cursola’s horrible def and he’s a special attacker. Although you could also go for Relaxed (+Def, -Speed) because his bad speed could be used to help him on a trick room team.
Btw, I know I used the pro-noun he, him a lot; plz don’t get salty at me. It was just easier to write that way.