@ Tarazuma
"Body: Mamanbo's body is shaped like an ACTUAL ocean sunfish. Luvdisc's body is shaped exactly like a HEART"
A symbolic heart, not an actual heart of course. Sunfish are in-fact shaped similarily to "symbolic hearts". Thats just pure coincidence though. GF meant this to be a sunfish just because sunfish are awesome like that. They didn't choose a sunfish to be a Luvdisc evo because it's resemblence to a heart. You are right about that I'm sure >.>
Mouth: Luvdisc has thin narrow lips that form the point of it's "heart" shape. Mamanbo has a flat mouth exactly like an ocean sunfish.
FACT: New pokemon are "generally" more realistic in terms of which features are included on the pokemon. Older generation pokemon in general over emphesized certain features for effect, while newer generation pokemon in general look more like the animal they represent. I can make a list to prove this. In Generation 3 it was acceptable for a sunfish like pokemon to be heart shaped rather than accurately modeled after a sunfish. However in this generation, everything looks more realistic. An evolution for Luvdisc would logically begin to look more like the real thing.
Eyes: Luvdisc has solid black eyes, Mamanbo has white eyes with a yellow iris, and purplish eyelids.
FACT: First stage pokemon generally have cute eyes like Luvdisc's to make them look more like a child. 2nd and 3rd stage pokemon generally have more anime-like eyes, to show that they are no longer childish. There are many contridictions to this in first gen, however since then this rule has been followed to some extent. Mamambo is meant to look feminine, just the suggestion of eyelashes.
Cheeks: Luvdisc has pink cheek spots, Mamanbo does not.
The pink spots on it's side were evidence that something might be in that position in a later evolution. In saying so, Mamambo coincidently has flippers in the exact same place as Luvdisc's pink spot.
Fins: Luvdisc has no fins, Mamanbo has dorsal fins and side fins.
Refer to above
Color: Luvdisc's entire body is a darker pink, except for it's lips. Mamanbo's body is a light pink, with slightly darker pink on it's fins.
Look at Mamambo's sprite, not it's artwork. The artwork for Mamambo has him in an awkward pose, his front side is shaded, resulting in a greyed down pink color. If you would look at the sprite on the other hand, it is vibrant pink, quite similar to Luvdisc's color if I might add.