This is Feebas. He is very rare in this game. If you need to SEE him to complete your pokedex, go to route 222 and battle either Fisherman Brett or Sailor Luther. If you want to catch him, you need a super rod and he can only be found on 4 random tiles in Mt. Coronet. The tiles randomize each day as well. If your planning on evolving it to Milotic, there are pretty specific guidelines, although you could SEE a Milotic after the elite four when you battle Champion Cynthia.
Feebas
No, there is not a Pokedex after the National Pokedex in Pokemon Diamond Version.
diamond pokedex number 80 is Barboach
Milotic
feebas
numbers 138 and 139 are Feebas and Milotic.
if you mean which Pokemon is #138 in Pokemon Emerald it is Jiggleypuff in the Hoenn Pokedex or Omanyte if you have the National Pokedex
Riolu
Oddish is the 43rd Pokemon.
in the national pokedex it is mackoke. if it is in the sinnoh pokedex it is buneary.
Number 33 is Golem on the Sinnoh Pokedex.
Well, since there is no number 117 in the local pokedex in Pokemon Diamond, we have to look into the national pokedex. In the national pokedex, number 117 is Seadra. Number 117 in the Sinnoh Pokedex is Wooper, can be found in the great marsh or on route 212