Do you mean...
Sinnoh Pokedex:
Barboach
Route 205 North, Route 210 North, Route 225, Route 227, Route 228, Ravaged Path, Oreburgh Gate, Eterna City, Great Marsh, Mt. Coronet (Fish With Good Rod)
National Pokedex:
Slowbro
Catch a Slowpoke in Route 205 North (PokeRadar) and raise it to level 37
if its the sinnoh dex its barboach and if its the national dex its slowbro.
Pokemon Number 169 in Platinum is Leafeon
Level 80! :D
Number 80 is Barboach, 3 trainers have 1 and they are Fisherman Cody who is within Route 209, Youngster Oliver who is in the Lost Tower and FAishman Travis who is on the south side of Route 212.
Pokemon number 151 is Manaphy
Arceaus (but you can only get it through events)
Unown
unown
No such Pokemon exists.
GLACEON
Glaceon
Snorunt