Quartz
Hero
In aggregate, half of the rest of the party, since the opponent is prone until their next turn when they stand up, not until the Rogue's next turn. Also, prone grants disadvantage to ranged attack rolls so it penalizes any characters doing that.
Yes, but if that person next to you is a Paladin, particularly a high-level Paladin, doing + 1d6 Radiant damage per hit plus Smite damage. Or a Fighter with multiple attacks.
And doesn't someone falling prone provoke a Reaction for extra smack-down sweetness?
Only if they are within 5 ft. Anyone attacking from range will be at disadvantage.
How about Reach weapons?