User blog comment:Kind-Hearted-One/Champion Descriptions: Let's do this/@comment-24430045-20150728220121/@comment-1920550-20150728232356

Assassins have extreme mobility with multiple spells of that nature or with low cooldown ones. Things like LeBlanc, Fizz, Zed, Kassadin, Akali, Ekko. Everything else can be seen as high mobility.

Difference is most marksmen don't have entire team compositions built around them being the sole damage carry on the team. Kog''Maw however is a case of extremes, with the highest pure damage potential in the game, but being incredibly fragille at the same time (he's not even made of glass, he a bloody paper cannon), both due to his low base health and resistances and his utter lack of self peel, it's meant to be a short way to make people realize the unique nature of this champion.