Snake's down special has him placing C4 on the ground that he can detonate by doing his down special again. I have seen it be placed on enemies before, and I have done it myself, but I can not do it consistently. Sometimes I will place it accidentally on an enemy while other times I will try to and not succeed. 

The [wiki](https://www.ssbwiki.com/Snake_(SSBU)#Special_Moves) says that you just need to be near to them to do it, but I feel that there is more to it, at least to doing it consistently.