Interesting Dispel Magic Questions

[Skrum]

Tentatively, I'd say that Shadow Blade would be both an object and a magical effect (it's taking concentration to maintain after all). DM does require that the caster target something, so the caster could either target the blade itself in which case it would be uncontroversially dispelled, or they could target the caster of the shadow blade, in which case it would also end since it's an ongoing magical effect (along with any other effects they are enjoying). I think?

I wouldn't object though to a GM that gave DM a more narrow, specific ruling, like "choose a single magical effect in range. End that effect." That would certainly make it more clear about what it did.