Super Mario Bros. D-Pad Controller (L) for Nintendo Switch
This has a D-Pad, instead of four individual directional buttons. The upside is that it makes some games, like 2-D fighters and shooters, a bit easier to play. The downside is that it is not a regular Joy Con, in that it can only be used when connected to your Switch in portable mode. Another thing to consider is the excess plastic around the release button on the back. With regular Joy Cons, you can use clip-on handles to make your Switch more comfortable to hold, but with this on instead of the standard one, most handles will no longer fit.
No. You can't use this unless its connected directly to the system.
Not a skin, this is a functional left Joy Con, though only when physically connected to a Switch. It does not work while detached nor does it have any additional features (rumble, motion, Amibo reader).