It's no secret that a select few of Super Smash Bros. characters can deal damage (albeit very little) using taunts. In fact, it's been the case since the very first iteration on the Nintendo 64, with Luigi's shyly executed kick being able to hurt opponents by up to a whopping 2%. With the arrival of Super Smash Bros. Brawl for the Wii, Solid Snake was discovered as the only other additional fighter capable of delivering damage by taunting, using his cardboard box. Again, the damage dealt was minuscule, but it could catch opponents by surprise if used correctly!
However, in Super Smash Bros. for 3DS & Wii U, Greninja became the third fighter in the franchise's history to harm opponents via taunting. Greninja's Down Taunt leads to the samurai frog shooting spurts of water from the palm of its hands, causing damage as well as achieving a similar effect to Mario's F.L.U.D.D. Down Special, pushing opponents away.
With that said, YouTuber Master0fHyrule has created a video of what damage percentage each fighter needs to reach before Greninja's Down Taunt can KO them. Yes, the level of damage each fighter needs to reach is improbable to occur in real battle, but if you're able to get an opponent to this percentage range and happen to be using Greninja, you've got an extra trick up your sleeve!
Check out the video below to see it in action against every Smash fighter. Master0fHyrule also states that he also tried this with Luigi's Down Taunt, and could not KO anyone despite reaching a damage percentage of 999 with each fighter. You'd probably think this makes Greninja's taunt more powerful than Luigi's, right? Well, try taking Luigi's Down Taunt while hanging off a ledge - we dare you.