Smoke Bomb

It draws in front of everything and it is fully opaque, so whatever is inside a cloud is hidden rather than dimmed. One is enough to bury a single player. Filling a room takes several, and the game caps how many particles can exist at once, so blanketing a whole screen is off the table no matter how many you throw.

They bounce and roll before settling, which means where you aim is not where the cloud ends up. Throw short and let them come to rest, or drop one at your feet when you want the smoke exactly where you are standing. Each one is spent after a single throw and cannot be picked back up.

Player versus player at close range. In a cramped arena a cloud hides where you are standing and buys a couple of seconds of guessing, which is often all a fight needs. Combine it with something that already makes you invisible, a stealth set bonus or a Psycho Knife, and the disappearance looks deliberate rather than lucky. Outside of that it is a party trick and a decent effect for a build.