Prinplup evolves into Empoleon at level 36.
You don't unless you evolve your piplup (level 16 i think). But, if you have a usb port and a usb wi-fi connection cord and do the set up, you can go to the gts and try to trade a Pokemon for a prinplup. Hope I helped!
It will evolve at level 48
it will evolve at level 21
Pachirisu does not evolve :(
Arbok does not evolve
level them up
level 44
at level 20
Level 40.
Level 10
level 25
Level 30