Second Stage
                                                                  The second stage of a digimon is after they hatch into little puffy pink creatures, some anyway. Like Konekomon
                                    hatches into a little red puppy-like creature. The only attack that the first stage digimon can do is blowing pink bubbles at the enemy called
                                    "Bubble Blast". Picture of second stage digimon.

                                                                 Third Stage
                                                                  Basically when the digimon has enough energy from his/her digi-destine or from food it has eaten it can digi-volve into
                                    it's third stage that is little more powerful. It looks more like it's fourth stage digi-volve but smaller and cuter. Like how Nekomon looks
                                    her smaller version of Tategamimon. Each third stage digimon has their own attack of their own, it could be element wise (fire, water, fish,
                                    etc.)  or if your digimon looks like a plant, anything that makes a plant dangereous.
                                    Example This is Agumon, his second digimon form was Koromon, link above picture. Can you tell the difference ?

                                                                Fourth Stage
                                                                 Digimon can only digi-volve when their digi-destine is in danger, all they have to say is their name-"digi-volve to" then
                                    their fourth stage name. They grow more powerful and take full appearance like from their third stage. Example : "Agumon digi-volve to
                                   Greymon".

                                                                Ultimate Stage
                                                                 Bear with me there's one more stage of a digimon, their ultimate stage. They digi-volve into their "grown up" stage but
                                    they can do with if the crest that their digi-destine have has a shiny tag with the symbol of the sun inside of the crest. It activates the power
                                    within the digi-mon. But if a digi-destine pushes their digimon too far to digi-volve to their ultimate stage they can digi-volve into evil digimon.
                                    Example of Greymon's ultimate stage, Metal Greymon.

                              All Digimon pictures were borrowed from "Unoffical Digimon Domain".