I played with a guy that has a moonball kick serve for a 2nd serve. Huge net clearance, a ton of spin that makes it bounce high almost straight up, and very little pace. A while ago I remember someone asking how to return a serve like that. Of course some players are able to easily attack it, but most try and mistime and end up backing up and hitting a neutral return. I wouldn't want to use a serve like that for every 2nd serve, but thought more variety is always good and it could be a good change of pace serve.