Brawlhalla

This achievement requires you to both dash jump and use ground pound attacks, which aren't immediately obvious as to what they are. Dash jumping occurs when you dash forward on the ground using either LT or RT and follow it immediately by a jump. This timing is a bit tricky at first, but you know you have gotten it when your character performs a shorter, faster jump than normal. I'd recommend testing this out a few times before trying it in a match online, since it's not too hard to do consistently with a little practice. A ground pound attack is unique to each weapon and occurs when you hit down and B/Y while in the air. Many weapons just lunge downward, so you've likely used this attack before without knowing it was called a ground pound attack. For this achievement, you must KO players by using the ground pound attack during the short dash jump. This is not super easy, because they must be at very high damage for it to work, unless you are hitting them while off stage. While any weapon works for this, I would recommend using the spear or other weapons that don't just do a downward thrust because the wider area to hit the opponents makes it much easier to hit them. The horizontal movement of the jump makes things tricky, so give yourself the most leeway when trying to hit them. Also, this must be done in a matchmaking game, so I'd recommend free for all for the multiple targets that can be at high damage. There were a few instances where I got double kills with my ground pound attack, so it can be very effective.

Just as a warning: I spent a few hours going for this achievement, and it definitely felt like I got more than 25 of these kills. I have no idea how well it correctly tracks your kills for this, so you may have to keep trying this until it pops. I also attempted this for a while with my second controller AFKing in free for all, but it did not seem like many, if any, of these kills on it were counting, so be aware of that if you want to try it that way.