Blackmore works as one of Funny Valentine's most trusted assassins. His Stand, Catch The Rainbow, manifests as a mask—and he's pretty clever about using that to his advantage. Since only Stand users can see his face behind it, he basically uses it as a built-in detector to figure out who can and can't see Stands.
The Stand itself gives him serious control over rain. He can freeze water droplets mid-air solid enough to walk on, or weaponize them as projectiles. It's the kind of ability that makes him especially dangerous in wet conditions, which doesn't hurt given where most of the story takes place.
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