Dolphin (Mario)

A Dolphin is a friend of Mario's in the game Super Mario World for the SNES. You'll only find these creatures on selected water levels. Once you do, you'll usually find them in groups as they jump out of the water, if you jump on one while in the air, it'll give you acess to higher grounds. They are always blue, and wear orange and red goggles. Apparently, in the Japanese version of Super Mario World, Yoshi was able to eat these friendly creatures.

Dolphins also appear quite alot in the Mario Party series. They appear in atleast three of them, includeing Mario Party 4, where he will allow characters to jump on him and let them collect coins. In Mario Party Advance, you had to help one of the Dolphins get his confidence back and tell jokes. In Mario Party 7, you are able to see Dolphins jump in the background at the File Select menu.

It should also be noted that in Super Mario Sunshine, Isle Delfino resembles a Dolphin.

Guppy from Super Mario Galaxy was originally going to be a dolphin that resembled the species from Super Mario World, though for whatever reason they changed him into a friend/foe shark.