The SkyKnife debuted in Ascent of the Red Sentients, Part 2. where Vert and Zoom fought Krytus and Kyrosys in the Battle Zone where Kyrosys was imprisoned. Upon Zoom's arrival, the vehicles fused and the two were briefly able to get an edge against the two Red Sentients.
It appeared again in Full Throttle. The two vehicles merged to get through spinning rings that blocked the way to a Satellite. The rings proved too fast for the SkyKnife, though, and they retreat, the vehicle defusing halfway back to the portal.
The SkyKnife was the main mode of transportation used for Vert and Zoom in The Shadow Zone. It took a few hits from the Shadow Speeders but still managed to stay together throughout the trip to the Shadow Zone and back to the Volcano Battle Zone. Vert called off the fusion as they headed back to the Hub.
It was used in Sol Survivor to follow Kytren's essence through the Multiverse to his Re-Spawn Chamber with Sol guiding them. However, they were led into a trap and the fusion broke off as Sol was about to self-destruct.
It was used for the currently final time in Get Zemerik to escape the Toborian Badlands. The vehicle defused after doing battle with some Alpha Sark, nearly causing Vert and the Saber to fall off a cliff.