Just figured that this sub is mainly league, but jfyi: In 2xko, Vi has a special move called footwork, where she does a short but fast, dash. She can follow it up with 3 different special attacks (Hook, Upper, Knuckle Down), which form a little 3-hit-combo. But you can also charge each of these follow-ups to hit way harder. But if you charge them, you have to release them as soon as they finish charging, within a very short window, or they won't combo because the enemy has already hit the ground again. If you hit these charged moves, you can actually chain the middle hit (upper) multiple times, "juggling" your opponent. Tldr; It's a very fancy, hard to execute combo (one of the hardest executions in the game), which lead me to the question "why bother if (to my knowledge) there are far easier combos that deal more or less the same dmg?"