>>13668889pokemon evolution: all pokemon start out in their base form, after they grow/mature/whatever enough they permanently "grow" into their evolved form, once they're evolved they stay like that forevever
digimon evolution: digimon go baby > intraining > rookie > champion > ultimate > mega
baby digimon are basically just blobs
in-training are more intricate blobs
rookies are the "normal" stage, a majority of digimon stay rookie forever
champion comes after rookie, for "normal"/"wild" digimon it can be hard to reach champion and its hardly guaranteed but if they do they usually stay like that forever unless they get killed, for digimon with human partners its basically a battle powerup using the humans energy to temporarily reach a higher form
ultimate is the same deal, human-partnered digimon can use digivices/crests/cards/whatever to go from champion to ultimate, usually at the cost of dropping back to in-training afterwards, whereas the few digimon who nautrally reach ultimate stay like that forever
mega is basically the holy shit deus ex machina transformation (in adventure it took a convoluted angel suicide arrow thing, in tamers they had to fuse with the humans)
the two biggest things to remember when you compare pokemon to digimon is that digimon evolution is temporary and reversible and digimon evolution is ridiculously inconsistent, the rules basically change every season and xros wars/fusion doesnt even have levels because it got to the point where there was just too much bullshit to handle
tl;dr digimon use digivices to temporarily grow up and become superpowered, pokemon naturally grow up and use mega stones to temporarily become superpowered
