I'm under oath not to tell you how good Diddy is.
I absolutely cannot inform you that Glide Tossing Bananas is one of the single greatest things in this game.
And under no circumstances am I allowed to explain that Diddy is a great character. That he has a very unique playstyle. has valid combos, and like Mario in Melee, doesn't have any impossible matchups, just matchups he really has to work for.
It would especially be breaking the oath if I told you to watch the video in this thread:
http://smashboards.com/showthread.php?t=184468
Since it's like an advertisement as to how good Diddy is (or can be).
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To be serious for a second, people can't tell you what character to play. Look at the characters that are winning tournaments (Or placing reasonably well), and decide for yourself. People can tell you all they want, but its up to you to find a character you're comfortable with.